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Subject[patch 1/3] vmscan: factor out page reference checks
Date
Moving the big conditional into its own predicate function makes the
code a bit easier to read and allows for better commenting on the
checks one-by-one.

This is just cleaning up, no semantics should have been changed.

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
---
mm/vmscan.c | 53 ++++++++++++++++++++++++++++++++++++++++-------------
1 files changed, 40 insertions(+), 13 deletions(-)
diff --git a/mm/vmscan.c b/mm/vmscan.c
index c26986c..c2db55b 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -579,6 +579,37 @@ redo:
put_page(page); /* drop ref from isolate */
}

+enum page_references {
+ PAGEREF_RECLAIM,
+ PAGEREF_RECLAIM_CLEAN,
+ PAGEREF_ACTIVATE,
+};
+
+static enum page_references page_check_references(struct page *page,
+ struct scan_control *sc)
+{
+ unsigned long vm_flags;
+ int referenced;
+
+ referenced = page_referenced(page, 1, sc->mem_cgroup, &vm_flags);
+ if (!referenced)
+ return PAGEREF_RECLAIM;
+
+ /* Lumpy reclaim - ignore references */
+ if (sc->order > PAGE_ALLOC_COSTLY_ORDER)
+ return PAGEREF_RECLAIM;
+
+ /* Mlock lost isolation race - let try_to_unmap() handle it */
+ if (vm_flags & VM_LOCKED)
+ return PAGEREF_RECLAIM;
+
+ if (page_mapping_inuse(page))
+ return PAGEREF_ACTIVATE;
+
+ /* Reclaim if clean, defer dirty pages to writeback */
+ return PAGEREF_RECLAIM_CLEAN;
+}
+
/*
* shrink_page_list() returns the number of reclaimed pages
*/
@@ -590,16 +621,15 @@ static unsigned long shrink_page_list(struct list_head *page_list,
struct pagevec freed_pvec;
int pgactivate = 0;
unsigned long nr_reclaimed = 0;
- unsigned long vm_flags;

cond_resched();

pagevec_init(&freed_pvec, 1);
while (!list_empty(page_list)) {
+ enum page_references references;
struct address_space *mapping;
struct page *page;
int may_enter_fs;
- int referenced;

cond_resched();

@@ -641,17 +671,14 @@ static unsigned long shrink_page_list(struct list_head *page_list,
goto keep_locked;
}

- referenced = page_referenced(page, 1,
- sc->mem_cgroup, &vm_flags);
- /*
- * In active use or really unfreeable? Activate it.
- * If page which have PG_mlocked lost isoltation race,
- * try_to_unmap moves it to unevictable list
- */
- if (sc->order <= PAGE_ALLOC_COSTLY_ORDER &&
- referenced && page_mapping_inuse(page)
- && !(vm_flags & VM_LOCKED))
+ references = page_check_references(page, sc);
+ switch (references) {
+ case PAGEREF_ACTIVATE:
goto activate_locked;
+ case PAGEREF_RECLAIM:
+ case PAGEREF_RECLAIM_CLEAN:
+ ; /* try to reclaim the page below */
+ }

/*
* Anonymous process memory has backing store?
@@ -685,7 +712,7 @@ static unsigned long shrink_page_list(struct list_head *page_list,
}

if (PageDirty(page)) {
- if (sc->order <= PAGE_ALLOC_COSTLY_ORDER && referenced)
+ if (references == PAGEREF_RECLAIM_CLEAN)
goto keep_locked;
if (!may_enter_fs)
goto keep_locked;
--
1.6.6.1


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