diff options
author | Nick Piggin <npiggin@suse.de> | 2008-07-26 02:45:30 (GMT) |
---|---|---|
committer | Linus Torvalds <torvalds@linux-foundation.org> | 2008-07-26 19:00:06 (GMT) |
commit | e286781d5f2e9c846e012a39653a166e9d31777d (patch) | |
tree | 14958fe6d8f3e0459c96c68b3034ea2433ab85ac /mm/filemap.c | |
parent | 47feff2c8eefe85099f87c43d3096855f0085ca0 (diff) | |
download | linux-e286781d5f2e9c846e012a39653a166e9d31777d.tar.xz |
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.c | 32 |
1 files changed, 18 insertions, 14 deletions
diff --git a/mm/filemap.c b/mm/filemap.c index 2d3ec1ff..4e182a9 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) |