From: Minchan Kim <minchan@kernel.org>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Matthew Wilcox <willy@infradead.org>, Jan Kara <jack@suse.cz>,
linux-mm <linux-mm@kvack.org>, Josef Bacik <josef@toxicpanda.com>,
Johannes Weiner <hannes@cmpxchg.org>,
LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] mm: fix long time stall from mm_populate
Date: Wed, 12 Feb 2020 15:12:10 -0800 [thread overview]
Message-ID: <20200212231210.GA233109@google.com> (raw)
In-Reply-To: <20200212142435.0b7e938fe8112fa35fcbcc71@linux-foundation.org>
On Wed, Feb 12, 2020 at 02:24:35PM -0800, Andrew Morton wrote:
> On Wed, 12 Feb 2020 11:53:22 -0800 Minchan Kim <minchan@kernel.org> wrote:
>
> > > That's definitely wrong. It'll clear PageReclaim and then pretend it did
> > > nothing wrong.
> > >
> > > return !PageWriteback(page) ||
> > > test_and_clear_bit(PG_reclaim, &page->flags);
> > >
> >
> > Much better, Thanks for the review, Matthew!
> > If there is no objection, I will send two patches to Andrew.
> > One is PageReadahead strict, the other is limit retry from mm_populate.
>
> With much more detailed changelogs, please!
>
> This all seems rather screwy. if a page is under writeback then it is
> uptodate and we should be able to fault it in immediately.
Hi Andrew,
This description in cover-letter will work? If so, I will add each part
below in each patch.
Subject: [PATCH 0/3] fixing mm_populate long stall
I got several reports major page fault takes several seconds sometime.
When I review drop mmap_sem in page fault hanlder, I found several bugs.
CPU 1 CPU 2
mm_populate
for ()
..
ret = populate_vma_page_range
__get_user_pages
faultin_page
handle_mm_fault
filemap_fault
do_async_mmap_readahead
shrink_page_list
pageout
SetPageReclaim(=SetPageReadahead)
writepage
SetPageWriteback
if (PageReadahead(page))
maybe_unlock_mmap_for_io
up_read(mmap_sem)
page_cache_async_readahead()
if (PageWriteback(page))
return;
here, since ret from populate_vma_page_range is zero,
the loop continue to run with same address with previous
iteration. It will repeat the loop until the page's
writeout is done(ie, PG_writeback or PG_reclaim clear).
We could fix the above specific case via adding PageWriteback. IOW,
ret = populate_vma_page_range
...
...
filemap_fault
do_async_mmap_readahead
if (!PageWriteback(page) && PageReadahead(page))
maybe_unlock_mmap_for_io
up_read(mmap_sem)
page_cache_async_readahead()
if (PageWriteback(page))
return;
That's a thing [3/3] is fixing here. Even though it could fix the
problem effectively, it has still livelock problem theoretically
because the page of faulty address could be reclaimed and then
allocated/become readahead marker on other CPUs during faulty
process is retrying in mm_populate's loop. [2/3] is fixing the
such livelock via limiting retry count.
There is another hole for the livelock or hang of the process as well
as ageWriteback - ra_pages.
mm_populate
for ()
..
ret = populate_vma_page_range
__get_user_pages
faultin_page
handle_mm_fault
filemap_fault
do_async_mmap_readahead
if (PageReadahead(page))
maybe_unlock_mmap_for_io
up_read(mmap_sem)
page_cache_async_readahead()
if (!ra->ra_pages)
return;
It will repeat the loop until ra->ra_pages become non-zero.
[1/3] is fixing the problem.
Jan Kara (1):
mm: Don't bother dropping mmap_sem for zero size readahead
Minchan Kim (2):
mm: fix long time stall from mm_populate
mm: make PageReadahead more strict
include/linux/page-flags.h | 28 ++++++++++++++++++++++++++--
mm/filemap.c | 2 +-
mm/gup.c | 9 +++++++--
mm/readahead.c | 6 ------
4 files changed, 34 insertions(+), 11 deletions(-)
--
2.25.0.225.g125e21ebc7-goog
next prev parent reply other threads:[~2020-02-12 23:12 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-11 0:19 [PATCH] mm: fix long time stall from mm_populate Minchan Kim
2020-02-11 1:10 ` Matthew Wilcox
2020-02-11 3:50 ` Minchan Kim
2020-02-11 3:54 ` Matthew Wilcox
2020-02-11 4:25 ` Minchan Kim
2020-02-11 12:23 ` Matthew Wilcox
2020-02-11 16:34 ` Minchan Kim
2020-02-11 17:28 ` Matthew Wilcox
2020-02-11 17:57 ` Minchan Kim
2020-02-12 10:18 ` Jan Kara
2020-02-12 17:40 ` Minchan Kim
2020-02-12 18:28 ` Matthew Wilcox
2020-02-12 19:53 ` Minchan Kim
2020-02-12 22:24 ` Andrew Morton
2020-02-12 23:12 ` Minchan Kim [this message]
2020-02-13 2:00 ` Andrew Morton
2020-02-13 17:24 ` Minchan Kim
2020-02-11 18:14 ` Yang Shi
2020-02-12 10:22 ` Jan Kara
2020-02-12 17:43 ` Minchan Kim
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