Messages in this thread Patch in this message | | | From | KOSAKI Motohiro <> | Subject | Re: [PATCH] NOMMU: Pages allocated to a ramfs inode's pagecache may get wrongly discarded | Date | Thu, 12 Mar 2009 10:04:41 +0900 (JST) |
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Hi
> >> Page reclaim shouldn't be even attempting to reclaim or write back > >> ramfs pagecache pages - reclaim can't possibly do anything with these > >> pages! > >> > >> Arguably those pages shouldn't be on the LRU at all, but we haven't > >> done that yet. > >> > >> Now, my problem is that I can't 100% be sure that we _ever_ implemented > >> this properly. ?I _think_ we did, in which case we later broke it. ?If > >> we've always been (stupidly) trying to pageout these pages then OK, I > >> guess your patch is a suitable 2.6.29 stopgap. > > > > OK, I can't find any code anywhere in which we excluded ramfs pages > > from consideration by page reclaim. ?How dumb. > > The ramfs considers it in just CONFIG_UNEVICTABLE_LRU case > It that case, ramfs_get_inode calls mapping_set_unevictable. > So, page reclaim can exclude ramfs pages by page_evictable. > It's problem .
Currently, CONFIG_UNEVICTABLE_LRU can't use on nommu machine because nobody of vmscan folk havbe nommu machine.
Yes, it is very stupid reason. _very_ welcome to tester! :)
David, Could you please try following patch if you have NOMMU machine? it is straightforward porting to nommu.
== Subject: [PATCH] remove to depend on MMU from CONFIG_UNEVICTABLE_LRU
logically, CONFIG_UNEVICTABLE_LRU doesn't depend on MMU. but current code does by mistake. fix it.
Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> --- mm/Kconfig | 1 - mm/nommu.c | 24 ++++++++++++++++++++++++ 2 files changed, 24 insertions(+), 1 deletion(-)
Index: b/mm/Kconfig =================================================================== --- a/mm/Kconfig 2008-12-28 20:55:23.000000000 +0900 +++ b/mm/Kconfig 2008-12-28 21:24:08.000000000 +0900 @@ -212,7 +212,6 @@ config VIRT_TO_BUS config UNEVICTABLE_LRU bool "Add LRU list to track non-evictable pages" default y - depends on MMU help Keeps unevictable pages off of the active and inactive pageout lists, so kswapd will not waste CPU time or have its balancing Index: b/mm/nommu.c =================================================================== --- a/mm/nommu.c 2008-12-25 08:26:37.000000000 +0900 +++ b/mm/nommu.c 2008-12-28 21:29:36.000000000 +0900 @@ -1521,3 +1521,27 @@ int access_process_vm(struct task_struct mmput(mm); return len; } + +/* + * LRU accounting for clear_page_mlock() + */ +void __clear_page_mlock(struct page *page) +{ + VM_BUG_ON(!PageLocked(page)); + + if (!page->mapping) { /* truncated ? */ + return; + } + + dec_zone_page_state(page, NR_MLOCK); + count_vm_event(UNEVICTABLE_PGCLEARED); + if (!isolate_lru_page(page)) { + putback_lru_page(page); + } else { + /* + * We lost the race. the page already moved to evictable list. + */ + if (PageUnevictable(page)) + count_vm_event(UNEVICTABLE_PGSTRANDED); + } +}
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