diff options
author | Nick Piggin <npiggin@suse.de> | 2008-07-25 22:45:30 -0400 |
---|---|---|
committer | Linus Torvalds <torvalds@linux-foundation.org> | 2008-07-26 15:00:06 -0400 |
commit | e286781d5f2e9c846e012a39653a166e9d31777d (patch) | |
tree | 14958fe6d8f3e0459c96c68b3034ea2433ab85ac /drivers | |
parent | 47feff2c8eefe85099f87c43d3096855f0085ca0 (diff) |
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 'drivers')
-rw-r--r-- | drivers/net/cassini.c | 12 |
1 files changed, 12 insertions, 0 deletions
diff --git a/drivers/net/cassini.c b/drivers/net/cassini.c index 83768df27806..f1936d51b458 100644 --- a/drivers/net/cassini.c +++ b/drivers/net/cassini.c | |||
@@ -576,6 +576,18 @@ static void cas_spare_recover(struct cas *cp, const gfp_t flags) | |||
576 | list_for_each_safe(elem, tmp, &list) { | 576 | list_for_each_safe(elem, tmp, &list) { |
577 | cas_page_t *page = list_entry(elem, cas_page_t, list); | 577 | cas_page_t *page = list_entry(elem, cas_page_t, list); |
578 | 578 | ||
579 | /* | ||
580 | * With the lockless pagecache, cassini buffering scheme gets | ||
581 | * slightly less accurate: we might find that a page has an | ||
582 | * elevated reference count here, due to a speculative ref, | ||
583 | * and skip it as in-use. Ideally we would be able to reclaim | ||
584 | * it. However this would be such a rare case, it doesn't | ||
585 | * matter too much as we should pick it up the next time round. | ||
586 | * | ||
587 | * Importantly, if we find that the page has a refcount of 1 | ||
588 | * here (our refcount), then we know it is definitely not inuse | ||
589 | * so we can reuse it. | ||
590 | */ | ||
579 | if (page_count(page->buffer) > 1) | 591 | if (page_count(page->buffer) > 1) |
580 | continue; | 592 | continue; |
581 | 593 | ||