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    SubjectRe: [RFC] memory hotremove patch take 2 [07/10] (delay freeing anon_vma)
    Delaying freeing anon_vma until migration finishes.

    We cannot trust page->mapping (of ANON) when page_mapcount(page) ==0.

    page migration puts page_mocount(page) to be 0. So we have to
    guarantee anon_vma pointed by page->mapping is valid by some hook.

    Usual page migration guarantees this by mm->sem. but we can't do it.
    So, just delaying freeing anon_vma.

    Signed-Off-By: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
    Signed-off-by: Yasunori Goto <y-goto@jp.fujitsu.com>

    include/linux/migrate.h | 2 ++
    include/linux/page_isolation.h | 14 ++++++++++++++
    include/linux/rmap.h | 22 ++++++++++++++++++++++
    mm/Kconfig | 12 ++++++++++++
    mm/memory_hotplug.c | 4 ++--
    mm/migrate.c | 37 +++++++++++++++++++++++++++++++------
    mm/rmap.c | 36 +++++++++++++++++++++++++++++++++++-
    7 files changed, 118 insertions(+), 9 deletions(-)

    Index: current_test/mm/migrate.c
    ===================================================================
    --- current_test.orig/mm/migrate.c 2007-05-08 15:06:50.000000000 +0900
    +++ current_test/mm/migrate.c 2007-05-08 15:08:24.000000000 +0900
    @@ -28,6 +28,7 @@
    #include <linux/mempolicy.h>
    #include <linux/vmalloc.h>
    #include <linux/security.h>
    +#include <linux/page_isolation.h>

    #include "internal.h"

    @@ -607,7 +608,7 @@ static int move_to_new_page(struct page
    * to the newly allocated page in newpage.
    */
    static int unmap_and_move(new_page_t get_new_page, unsigned long private,
    - struct page *page, int force)
    + struct page *page, int force, int flag)
    {
    int rc = 0;
    int *result = NULL;
    @@ -632,7 +633,10 @@ static int unmap_and_move(new_page_t get
    goto unlock;
    wait_on_page_writeback(page);
    }
    -
    + if (PageAnon(page) && is_migrate_nocontext(flag)) {
    + /* hold this anon_vma until remove_migration_ptes() finishes */
    + anon_vma_hold(page);
    + }
    /*
    * Establish migration ptes or remove ptes
    */
    @@ -640,8 +644,14 @@ static int unmap_and_move(new_page_t get
    if (!page_mapped(page))
    rc = move_to_new_page(newpage, page);

    - if (rc)
    + if (rc) {
    remove_migration_ptes(page, page);
    + if (PageAnon(page) && is_migrate_nocontext(flag))
    + anon_vma_release(page);
    + } else {
    + if (PageAnon(newpage) && is_migrate_nocontext(flag))
    + anon_vma_release(page);
    + }

    unlock:
    unlock_page(page);
    @@ -686,8 +696,8 @@ move_newpage:
    *
    * Return: Number of pages not migrated or error code.
    */
    -int migrate_pages(struct list_head *from,
    - new_page_t get_new_page, unsigned long private)
    +static int __migrate_pages(struct list_head *from,
    + new_page_t get_new_page, unsigned long private, int flag)
    {
    int retry = 1;
    int nr_failed = 0;
    @@ -707,7 +717,7 @@ int migrate_pages(struct list_head *from
    cond_resched();

    rc = unmap_and_move(get_new_page, private,
    - page, pass > 2);
    + page, pass > 2, flag);

    switch(rc) {
    case -ENOMEM:
    @@ -737,6 +747,21 @@ out:
    return nr_failed + retry;
    }

    +int migrate_pages(struct list_head *from,
    + new_page_t get_new_page, unsigned long private)
    +{
    + return __migrate_pages(from, get_new_page, private, 0);
    +}
    +
    +#ifdef CONFIG_MIGRATION_REMOVE
    +int migrate_pages_and_remove(struct list_head *from,
    + new_page_t get_new_page, unsigned long private)
    +{
    + return __migrate_pages(from, get_new_page, private,
    + MIGRATE_NOCONTEXT);
    +}
    +#endif
    +
    #ifdef CONFIG_NUMA
    /*
    * Move a list of individual pages
    Index: current_test/include/linux/rmap.h
    ===================================================================
    --- current_test.orig/include/linux/rmap.h 2007-05-08 15:06:49.000000000 +0900
    +++ current_test/include/linux/rmap.h 2007-05-08 15:08:07.000000000 +0900
    @@ -26,6 +26,9 @@
    struct anon_vma {
    spinlock_t lock; /* Serialize access to vma list */
    struct list_head head; /* List of private "related" vmas */
    +#ifdef CONFIG_MIGRATION_REMOVE
    + atomic_t hold; /* == 0 if we can free this immediately */
    +#endif
    };

    #ifdef CONFIG_MMU
    @@ -37,10 +40,14 @@ static inline struct anon_vma *anon_vma_
    return kmem_cache_alloc(anon_vma_cachep, GFP_KERNEL);
    }

    +#ifndef CONFIG_MIGRATION_REMOVE
    static inline void anon_vma_free(struct anon_vma *anon_vma)
    {
    kmem_cache_free(anon_vma_cachep, anon_vma);
    }
    +#else
    +extern void anon_vma_free(struct anon_vma *anon_vma);
    +#endif

    static inline void anon_vma_lock(struct vm_area_struct *vma)
    {
    @@ -75,6 +82,21 @@ void page_add_file_rmap(struct page *);
    void page_dup_rmap(struct page *page, struct vm_area_struct *vma, unsigned long address);
    void page_remove_rmap(struct page *, struct vm_area_struct *);

    +#ifdef CONFIG_MIGRATION_REMOVE
    +/*
    + * While Page migration without any process context, we doesn't have
    + * mm->sem. Because page->mapcount goes down to 0 while migration,
    + * we cannot trust page->mapping value.
    + * These two functions prevents anon_vma from being freed while
    + * migration.
    + */
    +void anon_vma_hold(struct page *page);
    +void anon_vma_release(struct page *page);
    +#else /* !CONFIG_MIGRATION_REMOVE */
    +#define anon_vma_hold(page) do{}while(0)
    +#define anon_vma_release(page) do{}while(0)
    +#endif /* CONFIG_MIGRATION_REMOVE */
    +
    /*
    * Called from mm/vmscan.c to handle paging out
    */
    Index: current_test/mm/rmap.c
    ===================================================================
    --- current_test.orig/mm/rmap.c 2007-05-08 15:06:50.000000000 +0900
    +++ current_test/mm/rmap.c 2007-05-08 15:08:07.000000000 +0900
    @@ -155,8 +155,9 @@ void anon_vma_unlink(struct vm_area_stru
    empty = list_empty(&anon_vma->head);
    spin_unlock(&anon_vma->lock);

    - if (empty)
    + if (empty) {
    anon_vma_free(anon_vma);
    + }
    }

    static void anon_vma_ctor(void *data, struct kmem_cache *cachep,
    @@ -1003,3 +1004,36 @@ int try_to_unmap(struct page *page, int
    return ret;
    }

    +#ifdef CONFIG_MIGRATION_REMOVE
    +
    +void anon_vma_free(struct anon_vma *anon)
    +{
    + if (atomic_read(&anon->hold) == 0) {
    + kmem_cache_free(anon_vma_cachep, anon);
    + }
    +}
    +
    +void anon_vma_hold(struct page *page)
    +{
    + struct anon_vma *anon_vma;
    + anon_vma = page_lock_anon_vma(page);
    + if (!anon_vma)
    + return;
    + atomic_set(&anon_vma->hold, 1);
    + spin_unlock(&anon_vma->lock);
    +}
    +
    +void anon_vma_release(struct page *page)
    +{
    + struct anon_vma *anon_vma;
    + int empty;
    + anon_vma = page_lock_anon_vma(page);
    + if (!anon_vma)
    + return;
    + atomic_set(&anon_vma->hold, 0);
    + empty = list_empty(&anon_vma->head);
    + spin_unlock(&anon_vma->lock);
    + if (empty)
    + anon_vma_free(anon_vma);
    +}
    +#endif
    Index: current_test/mm/Kconfig
    ===================================================================
    --- current_test.orig/mm/Kconfig 2007-05-08 15:08:06.000000000 +0900
    +++ current_test/mm/Kconfig 2007-05-08 15:08:24.000000000 +0900
    @@ -131,6 +131,7 @@ config MEMORY_HOTREMOVE
    depends on MEMORY_HOTPLUG_SPARSE
    select MIGRATION
    select PAGE_ISOLATION
    + select MIGRATION_REMOVE

    # Heavily threaded applications may benefit from splitting the mm-wide
    # page_table_lock, so that faults on different parts of the user address
    @@ -158,6 +159,17 @@ config MIGRATION
    example on NUMA systems to put pages nearer to the processors accessing
    the page.

    +config MIGRATION_REMOVE
    + bool "Page migration for memory remove"
    + def_bool y
    + depends on MEMORY_HOTREMOVE
    + help
    + When Memory-Hotremove is executed, page migraion runs.
    + But a process which does page migraion doesn't have context of
    + migration target pages. This has a small race condition.
    + If this config is selected, some workaround for fix them is enabled.
    + This may be add slight performance influence.
    +
    config RESOURCES_64BIT
    bool "64 bit Memory and IO resources (EXPERIMENTAL)" if (!64BIT && EXPERIMENTAL)
    default 64BIT
    Index: current_test/include/linux/migrate.h
    ===================================================================
    --- current_test.orig/include/linux/migrate.h 2007-05-08 15:06:49.000000000 +0900
    +++ current_test/include/linux/migrate.h 2007-05-08 15:08:07.000000000 +0900
    @@ -30,6 +30,8 @@ extern int putback_lru_pages(struct list
    extern int migrate_page(struct address_space *,
    struct page *, struct page *);
    extern int migrate_pages(struct list_head *l, new_page_t x, unsigned long);
    +extern int migrate_pages_and_remove(struct list_head *l,
    + new_page_t x, unsigned long);

    extern int fail_migrate_page(struct address_space *,
    struct page *, struct page *);
    Index: current_test/mm/memory_hotplug.c
    ===================================================================
    --- current_test.orig/mm/memory_hotplug.c 2007-05-08 15:08:06.000000000 +0900
    +++ current_test/mm/memory_hotplug.c 2007-05-08 15:08:07.000000000 +0900
    @@ -345,7 +345,7 @@ static int do_migrate_and_isolate_pages(
    if (!pfn_valid(pfn)) /* never happens in sparsemem */
    continue;
    page = pfn_to_page(pfn);
    - if (is_page_isolated(info,page))
    + if (PageReserved(page))
    continue;
    ret = isolate_lru_page(page, &source);

    @@ -367,7 +367,7 @@ static int do_migrate_and_isolate_pages(
    if (list_empty(&source))
    goto out;
    /* this function returns # of failed pages */
    - ret = migrate_pages(&source, hotremove_migrate_alloc,
    + ret = migrate_pages_and_remove(&source, hotremove_migrate_alloc,
    (unsigned long)info);
    out:
    return ret;
    Index: current_test/include/linux/page_isolation.h
    ===================================================================
    --- current_test.orig/include/linux/page_isolation.h 2007-05-08 15:08:05.000000000 +0900
    +++ current_test/include/linux/page_isolation.h 2007-05-08 15:08:24.000000000 +0900
    @@ -32,6 +32,13 @@ is_page_isolated(struct isolation_info *
    return 0;
    }

    +#define MIGRATE_NOCONTEXT 0x1
    +static inline int
    +is_migrate_nocontext(int flag)
    +{
    + return (flag & MIGRATE_NOCONTEXT) == MIGRATE_NOCONTEXT;
    +}
    +
    extern struct isolation_info *
    register_isolation(unsigned long start, unsigned long end);

    @@ -50,5 +57,12 @@ page_under_isolation(struct zone *zone,
    return 0;
    }

    +
    +static inline int
    +is_migrate_nocontext(int flag)
    +{
    + return 0;
    +}
    +
    #endif
    #endif
    --
    Yasunori Goto


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