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authorNick Piggin <npiggin@suse.de>2008-07-25 19:45:30 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2008-07-26 12:00:06 -0700
commite286781d5f2e9c846e012a39653a166e9d31777d (patch)
tree14958fe6d8f3e0459c96c68b3034ea2433ab85ac /mm/filemap.c
parent47feff2c8eefe85099f87c43d3096855f0085ca0 (diff)
downloadconfigs-e286781d5f2e9c846e012a39653a166e9d31777d.tar.gz
mm: speculative page references
If we can be sure that elevating the page_count on a pagecache page will pin it, we can speculatively run this operation, and subsequently check to see if we hit the right page rather than relying on holding a lock or otherwise pinning a reference to the page. This can be done if get_page/put_page behaves consistently throughout the whole tree (ie. if we "get" the page after it has been used for something else, we must be able to free it with a put_page). Actually, there is a period where the count behaves differently: when the page is free or if it is a constituent page of a compound page. We need an atomic_inc_not_zero operation to ensure we don't try to grab the page in either case. This patch introduces the core locking protocol to the pagecache (ie. adds page_cache_get_speculative, and tweaks some update-side code to make it work). Thanks to Hugh for pointing out an improvement to the algorithm setting page_count to zero when we have control of all references, in order to hold off speculative getters. [kamezawa.hiroyu@jp.fujitsu.com: fix migration_entry_wait()] [hugh@veritas.com: fix add_to_page_cache] [akpm@linux-foundation.org: repair a comment] Signed-off-by: Nick Piggin <npiggin@suse.de> Cc: Jeff Garzik <jeff@garzik.org> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> Cc: Paul Mackerras <paulus@samba.org> Cc: Hugh Dickins <hugh@veritas.com> Cc: "Paul E. McKenney" <paulmck@us.ibm.com> Reviewed-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Signed-off-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> Signed-off-by: Hugh Dickins <hugh@veritas.com> Acked-by: Nick Piggin <npiggin@suse.de> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/filemap.c')
-rw-r--r--mm/filemap.c32
1 files changed, 18 insertions, 14 deletions
diff --git a/mm/filemap.c b/mm/filemap.c
index 2d3ec1ffc66..4e182a9a14c 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -442,39 +442,43 @@ int filemap_write_and_wait_range(struct address_space *mapping,
}
/**
- * add_to_page_cache - add newly allocated pagecache pages
+ * add_to_page_cache_locked - add a locked page to the pagecache
* @page: page to add
* @mapping: the page's address_space
* @offset: page index
* @gfp_mask: page allocation mode
*
- * This function is used to add newly allocated pagecache pages;
- * the page is new, so we can just run SetPageLocked() against it.
- * The other page state flags were set by rmqueue().
- *
+ * This function is used to add a page to the pagecache. It must be locked.
* This function does not add the page to the LRU. The caller must do that.
*/
-int add_to_page_cache(struct page *page, struct address_space *mapping,
+int add_to_page_cache_locked(struct page *page, struct address_space *mapping,
pgoff_t offset, gfp_t gfp_mask)
{
- int error = mem_cgroup_cache_charge(page, current->mm,
+ int error;
+
+ VM_BUG_ON(!PageLocked(page));
+
+ error = mem_cgroup_cache_charge(page, current->mm,
gfp_mask & ~__GFP_HIGHMEM);
if (error)
goto out;
error = radix_tree_preload(gfp_mask & ~__GFP_HIGHMEM);
if (error == 0) {
+ page_cache_get(page);
+ page->mapping = mapping;
+ page->index = offset;
+
write_lock_irq(&mapping->tree_lock);
error = radix_tree_insert(&mapping->page_tree, offset, page);
- if (!error) {
- page_cache_get(page);
- SetPageLocked(page);
- page->mapping = mapping;
- page->index = offset;
+ if (likely(!error)) {
mapping->nrpages++;
__inc_zone_page_state(page, NR_FILE_PAGES);
- } else
+ } else {
+ page->mapping = NULL;
mem_cgroup_uncharge_cache_page(page);
+ page_cache_release(page);
+ }
write_unlock_irq(&mapping->tree_lock);
radix_tree_preload_end();
@@ -483,7 +487,7 @@ int add_to_page_cache(struct page *page, struct address_space *mapping,
out:
return error;
}
-EXPORT_SYMBOL(add_to_page_cache);
+EXPORT_SYMBOL(add_to_page_cache_locked);
int add_to_page_cache_lru(struct page *page, struct address_space *mapping,
pgoff_t offset, gfp_t gfp_mask)