On 2022/3/9 2:51, Yang Shi wrote: > On Tue, Mar 8, 2022 at 5:11 AM Miaohe Lin <linmiaohe@xxxxxxxxxx> wrote: >> >> On 2022/3/8 4:14, Yang Shi wrote: >>> On Mon, Mar 7, 2022 at 3:26 AM Miaohe Lin <linmiaohe@xxxxxxxxxx> wrote: >>>> >>>> On 2022/3/4 16:27, HORIGUCHI NAOYA(堀口 直也) wrote: >>>>> On Mon, Feb 28, 2022 at 10:02:43PM +0800, Miaohe Lin wrote: >>>>>> The dirty swapcache page is still residing in the swap cache after it's >>>>>> hwpoisoned. So there is always one extra refcount for swap cache. >>>>> >>>>> The diff seems fine at a glance, but let me have a few question to >>>>> understand the issue more. >>>>> >>>>> - Is the behavior described above the effect of recent change on shmem where >>>>> dirty pagecache is pinned on hwpoison (commit a76054266661 ("mm: shmem: >>>>> don't truncate page if memory failure happens"). Or the older kernels >>>>> behave as the same? >>>>> >>>>> - Is the behavior true for normal anonymous pages (not shmem pages)? >>>>> >>>> >>>> The behavior described above is aimed at swapcache not pagecache. So it should be >>>> irrelevant with the recent change on shmem. >>>> >>>> What I try to fix here is that me_swapcache_dirty holds one extra pin via SwapCache >>>> regardless of the return value of delete_from_lru_cache. We should try to report more >>>> accurate extra refcount for debugging purpose. >>> >>> I think you misunderstood the code. The delete_from_lru_cache() >>> returning 0 means the page was on LRU and isolated from LRU >>> successfully now. Returning -EIO means the page was not on LRU, so it >>> should have at least an extra pin on it. >>> >>> So MF_DELAYED means there is no other pin other than hwpoison and >>> swapcache which is expected, MF_FAILED means there might be extra >>> pins. >>> >>> The has_extra_refcount() raised error then there is *unexpected* refcount. >> >> Many thanks for your explanation. It seems you're right. If page is held on >> the lru_pvecs when we try to do delete_from_lru_cache, and after that it's >> drained to the lru list( so its refcnt might be 2 now). Then we might have >> the following complain if extra_pins is always true: >> "Memory failure: ... still referenced by 0 users\n" >> >> But it seems the origin code can not report the correct reason too because >> if we retry, page can be delete_from_lru_cache and we can succeed now. > > Retry is ok, but it seems overkilling to me IMHO. > Anyway, it seems I misunderstood the code. So I will drop this patch. Thanks for comment. >> >> Anyway, many thanks for pointing this out. >> >>> >>>> >>>>> I'm trying to test hwpoison hitting the dirty swapcache, but it seems that >>>>> in my testing memory_faliure() fails with "hwpoison: unhandlable page" >>>> >>>> Maybe memory_faliure is racing with page reclaim where page is isolated? >>>> >>>>> warning at get_any_page(). So I'm still not sure that me_pagecache_dirty() >>>>> fixes any visible problem. >>>> >>>> IIUC, me_pagecache_dirty can't do much except for the corresponding address_space supporting >>>> error_remove_page which can truncate the dirty pagecache page. But this may cause silent data >>>> loss. It's better to keep the page stay in the pagecache until the file is truncated, hole >>>> punched or removed as commit a76054266661 pointed out. >>>> >>>> Thanks. >>>> >>>>>> Thanks, >>>>> Naoya Horiguchi >>>>> >>>>>> >>>>>> Signed-off-by: Miaohe Lin <linmiaohe@xxxxxxxxxx> >>>>>> --- >>>>>> mm/memory-failure.c | 6 +----- >>>>>> 1 file changed, 1 insertion(+), 5 deletions(-) >>>>>> >>>>>> diff --git a/mm/memory-failure.c b/mm/memory-failure.c >>>>>> index 0d7c58340a98..5f9503573263 100644 >>>>>> --- a/mm/memory-failure.c >>>>>> +++ b/mm/memory-failure.c >>>>>> @@ -984,7 +984,6 @@ static int me_pagecache_dirty(struct page_state *ps, struct page *p) >>>>>> static int me_swapcache_dirty(struct page_state *ps, struct page *p) >>>>>> { >>>>>> int ret; >>>>>> - bool extra_pins = false; >>>>>> >>>>>> ClearPageDirty(p); >>>>>> /* Trigger EIO in shmem: */ >>>>>> @@ -993,10 +992,7 @@ static int me_swapcache_dirty(struct page_state *ps, struct page *p) >>>>>> ret = delete_from_lru_cache(p) ? MF_FAILED : MF_DELAYED; >>>>>> unlock_page(p); >>>>>> >>>>>> - if (ret == MF_DELAYED) >>>>>> - extra_pins = true; >>>>>> - >>>>>> - if (has_extra_refcount(ps, p, extra_pins)) >>>>>> + if (has_extra_refcount(ps, p, true)) >>>>>> ret = MF_FAILED; >>>>>> >>>>>> return ret; >>>>>> -- >>>>>> 2.23.0 >>>> >>>> >>> . >>> >> > . >