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Subject[patch 15/19] non-reclaimable mlocked pages
V2 -> V3:
+ rebase to 23-mm1 atop RvR's split lru series
+ fix page flags macros for *PageMlocked() when not configured.
+ ensure lru_add_drain_all() runs on all cpus when NORECLIM_MLOCK
configured. Was just for NUMA.

V1 -> V2:
+ moved this patch [and related patches] up to right after
ramdisk/ramfs and SHM_LOCKed patches.
+ add [back] missing put_page() in putback_lru_page().
This solved page leakage as seen by stats in previous
version.
+ fix up munlock_vma_page() to isolate page from lru
before calling try_to_unlock(). Think I detected a
race here.
+ use TestClearPageMlock() on old page in migrate.c's
migrate_page_copy() to clean up old page.
+ live dangerously: remove TestSetPageLocked() in
is_mlocked_vma()--should only be called on new pages in
the fault path--iff we chose to cull there [later patch].
+ Add PG_mlocked to free_pages_check() etc to detect mlock
state mismanagement.
NOTE: temporarily [???] commented out--tripping over it
under load. Why?

Rework of a patch by Nick Piggin -- part 1 of 2.

This patch:

1) defines the [CONFIG_]NORECLAIM_MLOCK sub-option and the
stub version of the mlock/noreclaim APIs when it's
not configured. Depends on [CONFIG_]NORECLAIM.

2) add yet another page flag--PG_mlocked--to indicate that
the page is locked for efficient testing in vmscan and,
optionally, fault path. This allows early culling of
nonreclaimable pages, preventing them from getting to
page_referenced()/try_to_unmap(). Also allows separate
accounting of mlock'd pages, as Nick's original patch
did.

Uses a bit available only to 64-bit systems.

Note: Nick's original mlock patch used a PG_mlocked
flag. I had removed this in favor of the PG_noreclaim
flag + an mlock_count [new page struct member]. I
restored the PG_mlocked flag to eliminate the new
count field.

3) add the mlock/noreclaim infrastructure to mm/mlock.c,
with internal APIs in mm/internal.h. This is a rework
of Nick's original patch to these files, taking into
account that mlocked pages are now kept on noreclaim
LRU list.

4) update vmscan.c:page_reclaimable() to check PageMlocked()
and, if vma passed in, the vm_flags. Note that the vma
will only be passed in for new pages in the fault path;
and then only if the "cull nonreclaimable pages in fault
path" patch is included.

5) add try_to_unlock() to rmap.c to walk a page's rmap and
ClearPageMlocked() if no other vmas have it mlocked.
Reuses as much of try_to_unmap() as possible. This
effectively replaces the use of one of the lru list links
as an mlock count. If this mechanism let's pages in mlocked
vmas leak through w/o PG_mlocked set [I don't know that it
does], we should catch them later in try_to_unmap(). One
hopes this will be rare, as it will be relatively expensive.

mm/internal.h and mm/mlock.c changes:
Originally Signed-off-by: Nick Piggin <npiggin@suse.de>

Signed-off-by: Lee Schermerhorn <lee.schermerhorn@hp.com>
Signed-off-by: Rik van Riel <riel@redhat.com>


Index: linux-2.6.24-rc6-mm1/mm/Kconfig
===================================================================
--- linux-2.6.24-rc6-mm1.orig/mm/Kconfig 2008-01-08 12:17:10.000000000 -0500
+++ linux-2.6.24-rc6-mm1/mm/Kconfig 2008-01-08 12:17:30.000000000 -0500
@@ -203,3 +203,17 @@ config NORECLAIM
may be non-reclaimable because: they are locked into memory, they
are anonymous pages for which no swap space exists, or they are anon
pages that are expensive to unmap [long anon_vma "related vma" list.]
+
+config NORECLAIM_MLOCK
+ bool "Exclude mlock'ed pages from reclaim"
+ depends on NORECLAIM
+ help
+ Treats mlock'ed pages as no-reclaimable. Removing these pages from
+ the LRU [in]active lists avoids the overhead of attempting to reclaim
+ them. Pages marked non-reclaimable for this reason will become
+ reclaimable again when the last mlock is removed.
+ when no swap space exists. Removing these pages from the LRU lists
+ avoids the overhead of attempting to reclaim them. Pages marked
+ non-reclaimable for this reason will become reclaimable again when/if
+ sufficient swap space is added to the system.
+
Index: linux-2.6.24-rc6-mm1/mm/internal.h
===================================================================
--- linux-2.6.24-rc6-mm1.orig/mm/internal.h 2008-01-08 12:08:02.000000000 -0500
+++ linux-2.6.24-rc6-mm1/mm/internal.h 2008-01-08 12:17:30.000000000 -0500
@@ -39,6 +39,64 @@ extern int isolate_lru_page(struct page
extern void __init __free_pages_bootmem(struct page *page,
unsigned int order);

+#ifdef CONFIG_NORECLAIM_MLOCK
+/*
+ * in mm/vmscan.c -- currently only used for NORECLAIM_MLOCK
+ */
+extern void putback_lru_page(struct page *page);
+
+/*
+ * called only for new pages in fault path
+ */
+extern int is_mlocked_vma(struct vm_area_struct *, struct page *);
+
+/*
+ * must be called with vma's mmap_sem held for read, and page locked.
+ */
+extern void mlock_vma_page(struct page *page);
+
+extern int __mlock_vma_pages_range(struct vm_area_struct *vma,
+ unsigned long start, unsigned long end, int lock);
+
+/*
+ * mlock all pages in this vma range. For mmap()/mremap()/...
+ */
+static inline void mlock_vma_pages_range(struct vm_area_struct *vma,
+ unsigned long start, unsigned long end)
+{
+ __mlock_vma_pages_range(vma, start, end, 1);
+}
+
+/*
+ * munlock range of pages. For munmap() and exit().
+ * Always called to operate on a full vma that is being unmapped.
+ */
+static inline void munlock_vma_pages_range(struct vm_area_struct *vma,
+ unsigned long start, unsigned long end)
+{
+// TODO: verify my assumption. Should we just drop the start/end args?
+ VM_BUG_ON(start != vma->vm_start || end != vma->vm_end);
+
+ vma->vm_flags &= ~VM_LOCKED; /* try_to_unlock() needs this */
+ __mlock_vma_pages_range(vma, start, end, 0);
+}
+
+extern void clear_page_mlock(struct page *page);
+
+#else /* CONFIG_NORECLAIM_MLOCK */
+static inline int is_mlocked_vma(struct vm_area_struct *v, struct page *p)
+{
+ return 0;
+}
+static inline void clear_page_mlock(struct page *page) { }
+static inline void mlock_vma_page(struct page *page) { }
+static inline void mlock_vma_pages_range(struct vm_area_struct *vma,
+ unsigned long start, unsigned long end) { }
+static inline void munlock_vma_pages_range(struct vm_area_struct *vma,
+ unsigned long start, unsigned long end) { }
+
+#endif /* CONFIG_NORECLAIM_MLOCK */
+
/*
* function for dealing with page's order in buddy system.
* zone->lock is already acquired when we use these.
Index: linux-2.6.24-rc6-mm1/mm/mlock.c
===================================================================
--- linux-2.6.24-rc6-mm1.orig/mm/mlock.c 2008-01-08 12:08:02.000000000 -0500
+++ linux-2.6.24-rc6-mm1/mm/mlock.c 2008-01-08 12:17:30.000000000 -0500
@@ -8,10 +8,16 @@
#include <linux/capability.h>
#include <linux/mman.h>
#include <linux/mm.h>
+#include <linux/swap.h>
+#include <linux/pagemap.h>
#include <linux/mempolicy.h>
#include <linux/syscalls.h>
#include <linux/sched.h>
#include <linux/module.h>
+#include <linux/rmap.h>
+#include <linux/mmzone.h>
+
+#include "internal.h"

int can_do_mlock(void)
{
@@ -23,19 +29,209 @@ int can_do_mlock(void)
}
EXPORT_SYMBOL(can_do_mlock);

+#ifdef CONFIG_NORECLAIM_MLOCK
+/*
+ * Mlocked pages are marked with PageMlocked() flag for efficient testing
+ * in vmscan and, possibly, the fault path.
+ *
+ * An mlocked page [PageMlocked(page)] is non-reclaimable. As such, it will
+ * be placed on the LRU "noreclaim" list, rather than the [in]active lists.
+ * The noreclaim list is an LRU sibling list to the [in]active lists.
+ * PageNoreclaim is set to indicate the non-reclaimable state.
+ *
+//TODO: no longer counting, but does this still apply to lazy setting
+// of PageMlocked() ??
+ * When lazy incrementing via vmscan, it is important to ensure that the
+ * vma's VM_LOCKED status is not concurrently being modified, otherwise we
+ * may have elevated mlock_count of a page that is being munlocked. So lazy
+ * mlocked must take the mmap_sem for read, and verify that the vma really
+ * is locked (see mm/rmap.c).
+ */
+
+/*
+ * Clear the page's PageMlocked(). This can be useful in a situation where
+ * we want to unconditionally remove a page from the pagecache.
+ *
+ * It is legal to call this function for any page, mlocked or not.
+ * If called for a page that is still mapped by mlocked vmas, all we do
+ * is revert to lazy LRU behaviour -- semantics are not broken.
+ */
+void clear_page_mlock(struct page *page)
+{
+ BUG_ON(!PageLocked(page));
+
+ if (likely(!PageMlocked(page)))
+ return;
+ ClearPageMlocked(page);
+ if (!isolate_lru_page(page))
+ putback_lru_page(page);
+}
+
+/*
+ * Mark page as mlocked if not already.
+ * If page on LRU, isolate and putback to move to noreclaim list.
+ */
+void mlock_vma_page(struct page *page)
+{
+ BUG_ON(!PageLocked(page));
+
+ if (!TestSetPageMlocked(page) && !isolate_lru_page(page))
+ putback_lru_page(page);
+}
+
+/*
+ * called from munlock()/munmap() path with page supposedly on the LRU.
+ *
+ * Note: unlike mlock_vma_page(), we can't just clear the PageMlocked
+ * [in try_to_unlock()] and then attempt to isolate the page. We must
+ * isolate the page() to keep others from messing with its noreclaim
+ * and mlocked state while trying to unlock. However, we pre-clear the
+ * mlocked state anyway as we might lose the isolation race and we might
+ * not get another chance to clear PageMlocked. If we successfully
+ * isolate the page and try_to_unlock() detects other VM_LOCKED vmas
+ * mapping the page, we just restore the PageMlocked state. If we lose
+ * the isolation race, and the page is mapped by other VM_LOCKED vmas,
+ * we'll detect this in try_to_unmap() and we'll call mlock_vma_page()
+ * above, if/when we try to reclaim the page.
+ */
+static void munlock_vma_page(struct page *page)
+{
+ BUG_ON(!PageLocked(page));
+
+ if (TestClearPageMlocked(page) && !isolate_lru_page(page)) {
+ if (try_to_unlock(page) == SWAP_MLOCK)
+ SetPageMlocked(page); /* still VM_LOCKED */
+ putback_lru_page(page);
+ }
+}
+
+/*
+ * Called in fault path via page_reclaimable() for a new page
+ * to determine if it's being mapped into a LOCKED vma.
+ * If so, mark page as mlocked.
+ */
+int is_mlocked_vma(struct vm_area_struct *vma, struct page *page)
+{
+ VM_BUG_ON(PageMlocked(page)); // TODO: needed?
+ VM_BUG_ON(PageLRU(page));
+
+ if (likely(!(vma->vm_flags & VM_LOCKED)))
+ return 0;
+
+ SetPageMlocked(page);
+ return 1;
+}
+
+/*
+ * mlock or munlock a range of pages in the vma depending on whether
+ * @lock is 1 or 0, respectively. @lock must match vm_flags VM_LOCKED
+ * state.
+TODO: we don't really need @lock, as we can determine it from vm_flags
+ *
+ * This takes care of making the pages present too.
+ *
+ * vma->vm_mm->mmap_sem must be held for write.
+ */
+int __mlock_vma_pages_range(struct vm_area_struct *vma,
+ unsigned long start, unsigned long end, int lock)
+{
+ struct mm_struct *mm = vma->vm_mm;
+ unsigned long addr = start;
+ struct page *pages[16]; /* 16 gives a reasonable batch */
+ int write = !!(vma->vm_flags & VM_WRITE);
+ int nr_pages;
+ int ret = 0;
+
+ BUG_ON(start & ~PAGE_MASK || end & ~PAGE_MASK);
+ VM_BUG_ON(lock != !!(vma->vm_flags & VM_LOCKED));
+
+ if (vma->vm_flags & VM_IO)
+ return ret;
+
+ lru_add_drain_all(); /* push cached pages to LRU */
+
+ nr_pages = (end - start) / PAGE_SIZE;
+
+ while (nr_pages > 0) {
+ int i;
+
+ cond_resched();
+
+ /*
+ * get_user_pages makes pages present if we are
+ * setting mlock.
+ */
+ ret = get_user_pages(current, mm, addr,
+ min_t(int, nr_pages, ARRAY_SIZE(pages)),
+ write, 0, pages, NULL);
+ if (ret < 0)
+ break;
+ if (ret == 0) {
+ /*
+ * We know the vma is there, so the only time
+ * we cannot get a single page should be an
+ * error (ret < 0) case.
+ */
+ WARN_ON(1);
+ ret = -EFAULT;
+ break;
+ }
+
+ lru_add_drain(); /* push cached pages to LRU */
+
+ for (i = 0; i < ret; i++) {
+ struct page *page = pages[i];
+
+ lock_page(page);
+ if (lock)
+ mlock_vma_page(page);
+ else
+ munlock_vma_page(page);
+ unlock_page(page);
+ put_page(page); /* ref from get_user_pages() */
+
+ addr += PAGE_SIZE; /* for next get_user_pages() */
+ nr_pages--;
+ }
+ }
+
+ lru_add_drain_all(); /* to update stats */
+
+ return ret;
+}
+
+#else /* CONFIG_NORECLAIM_MLOCK */
+
+/*
+ * Just make pages present if @lock true. No-op if unlocking.
+ */
+int __mlock_vma_pages_range(struct vm_area_struct *vma,
+ unsigned long start, unsigned long end, int lock)
+{
+ int ret = 0;
+
+ if (!lock || vma->vm_flags & VM_IO)
+ return ret;
+
+ return make_pages_present(start, end);
+}
+#endif /* CONFIG_NORECLAIM_MLOCK */
+
static int mlock_fixup(struct vm_area_struct *vma, struct vm_area_struct **prev,
unsigned long start, unsigned long end, unsigned int newflags)
{
- struct mm_struct * mm = vma->vm_mm;
+ struct mm_struct *mm = vma->vm_mm;
pgoff_t pgoff;
- int pages;
+ int nr_pages;
int ret = 0;
+ int lock;

if (newflags == vma->vm_flags) {
*prev = vma;
goto out;
}

+//TODO: linear_page_index() ? non-linear pages?
pgoff = vma->vm_pgoff + ((start - vma->vm_start) >> PAGE_SHIFT);
*prev = vma_merge(mm, *prev, start, end, newflags, vma->anon_vma,
vma->vm_file, pgoff, vma_policy(vma));
@@ -59,24 +255,25 @@ static int mlock_fixup(struct vm_area_st
}

success:
+ lock = !!(newflags & VM_LOCKED);
+
+ /*
+ * Keep track of amount of locked VM.
+ */
+ nr_pages = (end - start) >> PAGE_SHIFT;
+ if (!lock)
+ nr_pages = -nr_pages;
+ mm->locked_vm += nr_pages;
+
/*
* vm_flags is protected by the mmap_sem held in write mode.
* It's okay if try_to_unmap_one unmaps a page just after we
- * set VM_LOCKED, make_pages_present below will bring it back.
+ * set VM_LOCKED, __mlock_vma_pages_range will bring it back.
*/
vma->vm_flags = newflags;

- /*
- * Keep track of amount of locked VM.
- */
- pages = (end - start) >> PAGE_SHIFT;
- if (newflags & VM_LOCKED) {
- pages = -pages;
- if (!(newflags & VM_IO))
- ret = make_pages_present(start, end);
- }
+ __mlock_vma_pages_range(vma, start, end, lock);

- mm->locked_vm -= pages;
out:
if (ret == -ENOMEM)
ret = -EAGAIN;
Index: linux-2.6.24-rc6-mm1/mm/vmscan.c
===================================================================
--- linux-2.6.24-rc6-mm1.orig/mm/vmscan.c 2008-01-08 12:17:25.000000000 -0500
+++ linux-2.6.24-rc6-mm1/mm/vmscan.c 2008-01-08 12:17:30.000000000 -0500
@@ -887,6 +887,44 @@ int isolate_lru_page(struct page *page)
return ret;
}

+#ifdef CONFIG_NORECLAIM_MLOCK
+/**
+ * putback_lru_page(@page)
+ *
+ * Add previously isolated @page to appropriate LRU list.
+ * Page may still be non-reclaimable for other reasons.
+ *
+ * The vmstat page counts corresponding to the list on which the page
+ * will be placed will be incremented.
+ *
+ * lru_lock must not be held, interrupts must be enabled.
+ */
+void putback_lru_page(struct page *page)
+{
+ struct zone *zone = page_zone(page);
+ int lru = LRU_INACTIVE_ANON;
+
+ VM_BUG_ON(PageLRU(page));
+
+ ClearPageNoreclaim(page);
+ ClearPageActive(page);
+
+ spin_lock_irq(&zone->lru_lock);
+ if (page_reclaimable(page, NULL)) {
+ lru += page_file_cache(page);
+ } else {
+ lru = LRU_NORECLAIM;
+ SetPageNoreclaim(page);
+ }
+
+ SetPageLRU(page);
+ add_page_to_lru_list(zone, page, lru);
+ put_page(page); /* drop ref from isolate */
+
+ spin_unlock_irq(&zone->lru_lock);
+}
+#endif
+
/*
* shrink_inactive_list() is a helper for shrink_zone(). It returns the number
* of reclaimed pages
@@ -2255,10 +2293,11 @@ int zone_reclaim(struct zone *zone, gfp_
*
* @page - page to test
* @vma - vm area in which page is/will be mapped. May be NULL.
- * If !NULL, called from fault path.
+ * If !NULL, called from fault path for a new page.
*
* Reasons page might not be reclaimable:
- * + page's mapping marked non-reclaimable
+ * 1) page's mapping marked non-reclaimable
+ * 2) page is mlock'ed into memory.
* TODO - later patches
*
* TODO: specify locking assumptions
@@ -2271,6 +2310,11 @@ int page_reclaimable(struct page *page,
if (mapping_non_reclaimable(page_mapping(page)))
return 0;

+#ifdef CONFIG_NORECLAIM_MLOCK
+ if (PageMlocked(page) || (vma && is_mlocked_vma(vma, page)))
+ return 0;
+#endif
+
/* TODO: test page [!]reclaimable conditions */

return 1;
Index: linux-2.6.24-rc6-mm1/include/linux/page-flags.h
===================================================================
--- linux-2.6.24-rc6-mm1.orig/include/linux/page-flags.h 2008-01-08 12:17:10.000000000 -0500
+++ linux-2.6.24-rc6-mm1/include/linux/page-flags.h 2008-01-08 12:17:30.000000000 -0500
@@ -110,6 +110,7 @@
#define PG_uncached 31 /* Page has been mapped as uncached */

#define PG_noreclaim 30 /* Page is "non-reclaimable" */
+#define PG_mlocked 29 /* Page is vma mlocked */
#endif

/*
@@ -163,6 +164,7 @@ static inline void SetPageUptodate(struc
#define SetPageActive(page) set_bit(PG_active, &(page)->flags)
#define ClearPageActive(page) clear_bit(PG_active, &(page)->flags)
#define __ClearPageActive(page) __clear_bit(PG_active, &(page)->flags)
+#define TestSetPageActive(page) test_and_set_bit(PG_active, &(page)->flags)
#define TestClearPageActive(page) test_and_clear_bit(PG_active, &(page)->flags)

#define PageSlab(page) test_bit(PG_slab, &(page)->flags)
@@ -270,8 +272,17 @@ static inline void __ClearPageTail(struc
#define SetPageNoreclaim(page) set_bit(PG_noreclaim, &(page)->flags)
#define ClearPageNoreclaim(page) clear_bit(PG_noreclaim, &(page)->flags)
#define __ClearPageNoreclaim(page) __clear_bit(PG_noreclaim, &(page)->flags)
-#define TestClearPageNoreclaim(page) test_and_clear_bit(PG_noreclaim, \
- &(page)->flags)
+#define TestClearPageNoreclaim(page) \
+ test_and_clear_bit(PG_noreclaim, &(page)->flags)
+#ifdef CONFIG_NORECLAIM_MLOCK
+#define PageMlocked(page) test_bit(PG_mlocked, &(page)->flags)
+#define SetPageMlocked(page) set_bit(PG_mlocked, &(page)->flags)
+#define ClearPageMlocked(page) clear_bit(PG_mlocked, &(page)->flags)
+#define __ClearPageMlocked(page) __clear_bit(PG_mlocked, &(page)->flags)
+#define TestSetPageMlocked(page) test_and_set_bit(PG_mlocked, &(page)->flags)
+#define TestClearPageMlocked(page) \
+ test_and_clear_bit(PG_mlocked, &(page)->flags)
+#endif
#else
#define PageNoreclaim(page) 0
#define SetPageNoreclaim(page)
@@ -279,6 +290,14 @@ static inline void __ClearPageTail(struc
#define __ClearPageNoreclaim(page)
#define TestClearPageNoreclaim(page) 0
#endif
+#ifndef CONFIG_NORECLAIM_MLOCK
+#define PageMlocked(page) 0
+#define SetPageMlocked(page)
+#define ClearPageMlocked(page)
+#define __ClearPageMlocked(page)
+#define TestSetPageMlocked(page) 0
+#define TestClearPageMlocked(page) 0
+#endif

#define PageUncached(page) test_bit(PG_uncached, &(page)->flags)
#define SetPageUncached(page) set_bit(PG_uncached, &(page)->flags)
Index: linux-2.6.24-rc6-mm1/include/linux/rmap.h
===================================================================
--- linux-2.6.24-rc6-mm1.orig/include/linux/rmap.h 2008-01-08 12:08:02.000000000 -0500
+++ linux-2.6.24-rc6-mm1/include/linux/rmap.h 2008-01-08 12:17:30.000000000 -0500
@@ -109,6 +109,17 @@ unsigned long page_address_in_vma(struct
*/
int page_mkclean(struct page *);

+#ifdef CONFIG_NORECLAIM_MLOCK
+/*
+ * called in munlock()/munmap() path to check for other vmas holding
+ * the page mlocked.
+ */
+int try_to_unlock(struct page *);
+#define TRY_TO_UNLOCK 1
+#else
+#define TRY_TO_UNLOCK 0 /* for compiler -- dead code elimination */
+#endif
+
#else /* !CONFIG_MMU */

#define anon_vma_init() do {} while (0)
@@ -132,5 +143,6 @@ static inline int page_mkclean(struct pa
#define SWAP_SUCCESS 0
#define SWAP_AGAIN 1
#define SWAP_FAIL 2
+#define SWAP_MLOCK 3

#endif /* _LINUX_RMAP_H */
Index: linux-2.6.24-rc6-mm1/mm/rmap.c
===================================================================
--- linux-2.6.24-rc6-mm1.orig/mm/rmap.c 2008-01-08 12:08:02.000000000 -0500
+++ linux-2.6.24-rc6-mm1/mm/rmap.c 2008-01-08 12:17:30.000000000 -0500
@@ -52,6 +52,8 @@

#include <asm/tlbflush.h>

+#include "internal.h"
+
struct kmem_cache *anon_vma_cachep;

/* This must be called under the mmap_sem. */
@@ -284,10 +286,17 @@ static int page_referenced_one(struct pa
if (!pte)
goto out;

+ /*
+ * Don't want to elevate referenced for mlocked page that gets this far,
+ * in order that it progresses to try_to_unmap and is moved to the
+ * noreclaim list.
+ */
if (vma->vm_flags & VM_LOCKED) {
- referenced++;
*mapcount = 1; /* break early from loop */
- } else if (ptep_clear_flush_young(vma, address, pte))
+ goto out_unmap;
+ }
+
+ if (ptep_clear_flush_young(vma, address, pte))
referenced++;

/* Pretend the page is referenced if the task has the
@@ -296,6 +305,7 @@ static int page_referenced_one(struct pa
rwsem_is_locked(&mm->mmap_sem))
referenced++;

+out_unmap:
(*mapcount)--;
pte_unmap_unlock(pte, ptl);
out:
@@ -384,11 +394,6 @@ static int page_referenced_file(struct p
*/
if (mem_cont && (mm_cgroup(vma->vm_mm) != mem_cont))
continue;
- if ((vma->vm_flags & (VM_LOCKED|VM_MAYSHARE))
- == (VM_LOCKED|VM_MAYSHARE)) {
- referenced++;
- break;
- }
referenced += page_referenced_one(page, vma, &mapcount);
if (!mapcount)
break;
@@ -712,10 +717,15 @@ static int try_to_unmap_one(struct page
* If it's recently referenced (perhaps page_referenced
* skipped over this mm) then we should reactivate it.
*/
- if (!migration && ((vma->vm_flags & VM_LOCKED) ||
- (ptep_clear_flush_young(vma, address, pte)))) {
- ret = SWAP_FAIL;
- goto out_unmap;
+ if (!migration) {
+ if (vma->vm_flags & VM_LOCKED) {
+ ret = SWAP_MLOCK;
+ goto out_unmap;
+ }
+ if (ptep_clear_flush_young(vma, address, pte)) {
+ ret = SWAP_FAIL;
+ goto out_unmap;
+ }
}

/* Nuke the page table entry. */
@@ -797,6 +807,10 @@ out:
* For very sparsely populated VMAs this is a little inefficient - chances are
* there there won't be many ptes located within the scan cluster. In this case
* maybe we could scan further - to the end of the pte page, perhaps.
+ *
+TODO: still accurate with noreclaim infrastructure?
+ * Mlocked pages also aren't handled very well at the moment: they aren't
+ * moved off the LRU like they are for linear pages.
*/
#define CLUSTER_SIZE min(32*PAGE_SIZE, PMD_SIZE)
#define CLUSTER_MASK (~(CLUSTER_SIZE - 1))
@@ -868,10 +882,28 @@ static void try_to_unmap_cluster(unsigne
pte_unmap_unlock(pte - 1, ptl);
}

-static int try_to_unmap_anon(struct page *page, int migration)
+/**
+ * try_to_unmap_anon - unmap or unlock anonymous page using the object-based
+ * rmap method
+ * @page: the page to unmap/unlock
+ * @unlock: request for unlock rather than unmap [unlikely]
+ * @migration: unmapping for migration - ignored if @unlock
+ *
+ * Find all the mappings of a page using the mapping pointer and the vma chains
+ * contained in the anon_vma struct it points to.
+ *
+ * This function is only called from try_to_unmap/try_to_unlock for
+ * anonymous pages.
+ * When called from try_to_unlock(), the mmap_sem of the mm containing the vma
+ * where the page was found will be held for write. So, we won't recheck
+ * vm_flags for that VMA. That should be OK, because that vma shouldn't be
+ * 'LOCKED.
+ */
+static int try_to_unmap_anon(struct page *page, int unlock, int migration)
{
struct anon_vma *anon_vma;
struct vm_area_struct *vma;
+ unsigned int mlocked = 0;
int ret = SWAP_AGAIN;

anon_vma = page_lock_anon_vma(page);
@@ -879,25 +911,53 @@ static int try_to_unmap_anon(struct page
return ret;

list_for_each_entry(vma, &anon_vma->head, anon_vma_node) {
- ret = try_to_unmap_one(page, vma, migration);
+ if (TRY_TO_UNLOCK && unlikely(unlock)) {
+ if (!(vma->vm_flags & VM_LOCKED))
+ continue; /* must visit all vmas */
+ mlocked++;
+ break; /* no need to look further */
+ } else
+ ret = try_to_unmap_one(page, vma, migration);
if (ret == SWAP_FAIL || !page_mapped(page))
break;
+ if (ret == SWAP_MLOCK) {
+ if (down_read_trylock(&vma->vm_mm->mmap_sem)) {
+ if (vma->vm_flags & VM_LOCKED) {
+ mlock_vma_page(page);
+ mlocked++;
+ }
+ up_read(&vma->vm_mm->mmap_sem);
+ }
+ }
}
-
page_unlock_anon_vma(anon_vma);
+
+ if (mlocked)
+ ret = SWAP_MLOCK;
+ else if (ret == SWAP_MLOCK)
+ ret = SWAP_AGAIN;
+
return ret;
}

/**
- * try_to_unmap_file - unmap file page using the object-based rmap method
- * @page: the page to unmap
+ * try_to_unmap_file - unmap or unlock file page using the object-based
+ * rmap method
+ * @page: the page to unmap/unlock
+ * @unlock: request for unlock rather than unmap [unlikely]
+ * @migration: unmapping for migration - ignored if @unlock
*
* Find all the mappings of a page using the mapping pointer and the vma chains
* contained in the address_space struct it points to.
*
- * This function is only called from try_to_unmap for object-based pages.
+ * This function is only called from try_to_unmap/try_to_unlock for
+ * object-based pages.
+ * When called from try_to_unlock(), the mmap_sem of the mm containing the vma
+ * where the page was found will be held for write. So, we won't recheck
+ * vm_flags for that VMA. That should be OK, because that vma shouldn't be
+ * 'LOCKED.
*/
-static int try_to_unmap_file(struct page *page, int migration)
+static int try_to_unmap_file(struct page *page, int unlock, int migration)
{
struct address_space *mapping = page->mapping;
pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
@@ -908,19 +968,46 @@ static int try_to_unmap_file(struct page
unsigned long max_nl_cursor = 0;
unsigned long max_nl_size = 0;
unsigned int mapcount;
+ unsigned int mlocked = 0;

spin_lock(&mapping->i_mmap_lock);
vma_prio_tree_foreach(vma, &iter, &mapping->i_mmap, pgoff, pgoff) {
- ret = try_to_unmap_one(page, vma, migration);
+ if (TRY_TO_UNLOCK && unlikely(unlock)) {
+ if (!(vma->vm_flags & VM_LOCKED))
+ continue; /* must visit all vmas */
+ mlocked++;
+ break; /* no need to look further */
+ } else
+ ret = try_to_unmap_one(page, vma, migration);
if (ret == SWAP_FAIL || !page_mapped(page))
goto out;
+ if (ret == SWAP_MLOCK) {
+ if (down_read_trylock(&vma->vm_mm->mmap_sem)) {
+ if (vma->vm_flags & VM_LOCKED) {
+ mlock_vma_page(page);
+ mlocked++;
+ }
+ up_read(&vma->vm_mm->mmap_sem);
+ }
+ if (unlikely(unlock))
+ break; /* stop on 1st mlocked vma */
+ }
}

+ if (mlocked)
+ goto out;
+
if (list_empty(&mapping->i_mmap_nonlinear))
goto out;

list_for_each_entry(vma, &mapping->i_mmap_nonlinear,
shared.vm_set.list) {
+ if (TRY_TO_UNLOCK && unlikely(unlock)) {
+ if (!(vma->vm_flags & VM_LOCKED))
+ continue; /* must visit all vmas */
+ mlocked++;
+ goto out; /* no need to look further */
+ }
if ((vma->vm_flags & VM_LOCKED) && !migration)
continue;
cursor = (unsigned long) vma->vm_private_data;
@@ -955,8 +1042,6 @@ static int try_to_unmap_file(struct page
do {
list_for_each_entry(vma, &mapping->i_mmap_nonlinear,
shared.vm_set.list) {
- if ((vma->vm_flags & VM_LOCKED) && !migration)
- continue;
cursor = (unsigned long) vma->vm_private_data;
while ( cursor < max_nl_cursor &&
cursor < vma->vm_end - vma->vm_start) {
@@ -981,6 +1066,10 @@ static int try_to_unmap_file(struct page
vma->vm_private_data = NULL;
out:
spin_unlock(&mapping->i_mmap_lock);
+ if (mlocked)
+ ret = SWAP_MLOCK;
+ else if (ret == SWAP_MLOCK)
+ ret = SWAP_AGAIN;
return ret;
}

@@ -995,6 +1084,7 @@ out:
* SWAP_SUCCESS - we succeeded in removing all mappings
* SWAP_AGAIN - we missed a mapping, try again later
* SWAP_FAIL - the page is unswappable
+ * SWAP_MLOCK - page is mlocked.
*/
int try_to_unmap(struct page *page, int migration)
{
@@ -1003,12 +1093,32 @@ int try_to_unmap(struct page *page, int
BUG_ON(!PageLocked(page));

if (PageAnon(page))
- ret = try_to_unmap_anon(page, migration);
+ ret = try_to_unmap_anon(page, 0, migration);
else
- ret = try_to_unmap_file(page, migration);
-
- if (!page_mapped(page))
+ ret = try_to_unmap_file(page, 0, migration);
+ if (ret != SWAP_MLOCK && !page_mapped(page))
ret = SWAP_SUCCESS;
return ret;
}

+#ifdef CONFIG_NORECLAIM_MLOCK
+/**
+ * try_to_unlock - Check page's rmap for other vma's holding page locked.
+ * @page: the page to be unlocked. will be returned with PG_mlocked
+ * cleared if no vmas are VM_LOCKED.
+ *
+ * Return values are:
+ *
+ * SWAP_SUCCESS - no vma's holding page locked.
+ * SWAP_MLOCK - page is mlocked.
+ */
+int try_to_unlock(struct page *page)
+{
+ VM_BUG_ON(!PageLocked(page) || PageLRU(page));
+
+ if (PageAnon(page))
+ return(try_to_unmap_anon(page, 1, 0));
+ else
+ return(try_to_unmap_file(page, 1, 0));
+}
+#endif
Index: linux-2.6.24-rc6-mm1/mm/migrate.c
===================================================================
--- linux-2.6.24-rc6-mm1.orig/mm/migrate.c 2008-01-08 12:17:10.000000000 -0500
+++ linux-2.6.24-rc6-mm1/mm/migrate.c 2008-01-08 12:17:30.000000000 -0500
@@ -366,6 +366,9 @@ static void migrate_page_copy(struct pag
set_page_dirty(newpage);
}

+ if (TestClearPageMlocked(page))
+ SetPageMlocked(newpage);
+
#ifdef CONFIG_SWAP
ClearPageSwapCache(page);
#endif
Index: linux-2.6.24-rc6-mm1/mm/page_alloc.c
===================================================================
--- linux-2.6.24-rc6-mm1.orig/mm/page_alloc.c 2008-01-08 12:17:14.000000000 -0500
+++ linux-2.6.24-rc6-mm1/mm/page_alloc.c 2008-01-08 12:17:30.000000000 -0500
@@ -257,6 +257,7 @@ static void bad_page(struct page *page)
1 << PG_swapcache |
1 << PG_writeback |
1 << PG_swapbacked |
+ 1 << PG_mlocked |
1 << PG_buddy );
set_page_count(page, 0);
reset_page_mapcount(page);
@@ -488,6 +489,9 @@ static inline int free_pages_check(struc
#ifdef CONFIG_NORECLAIM
1 << PG_noreclaim |
#endif
+// TODO: always trip this under heavy workloads.
+// Why isn't this being cleared on last unmap/unlock?
+// 1 << PG_mlocked |
1 << PG_buddy ))))
bad_page(page);
if (PageDirty(page))
@@ -644,6 +648,8 @@ static int prep_new_page(struct page *pa
1 << PG_writeback |
1 << PG_reserved |
1 << PG_swapbacked |
+//TODO: why hitting this?
+// 1 << PG_mlocked |
1 << PG_buddy ))))
bad_page(page);

@@ -656,7 +662,9 @@ static int prep_new_page(struct page *pa

page->flags &= ~(1 << PG_uptodate | 1 << PG_error | 1 << PG_readahead |
1 << PG_referenced | 1 << PG_arch_1 |
- 1 << PG_owner_priv_1 | 1 << PG_mappedtodisk);
+ 1 << PG_owner_priv_1 | 1 << PG_mappedtodisk |
+//TODO take care of it here, for now.
+ 1 << PG_mlocked );
set_page_private(page, 0);
set_page_refcounted(page);

Index: linux-2.6.24-rc6-mm1/mm/swap.c
===================================================================
--- linux-2.6.24-rc6-mm1.orig/mm/swap.c 2008-01-08 12:17:10.000000000 -0500
+++ linux-2.6.24-rc6-mm1/mm/swap.c 2008-01-08 12:17:30.000000000 -0500
@@ -346,7 +346,7 @@ void lru_add_drain(void)
put_cpu();
}

-#ifdef CONFIG_NUMA
+#if defined(CONFIG_NUMA) || defined(CONFIG_NORECLAIM_MLOCK)
static void lru_add_drain_per_cpu(struct work_struct *dummy)
{
lru_add_drain();
--
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