From: Matthew Wilcox <willy@infradead.org>
To: Minchan Kim <minchan@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>,
linux-mm <linux-mm@kvack.org>, Josef Bacik <josef@toxicpanda.com>,
Johannes Weiner <hannes@cmpxchg.org>, Jan Kara <jack@suse.cz>,
LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] mm: fix long time stall from mm_populate
Date: Tue, 11 Feb 2020 04:23:23 -0800 [thread overview]
Message-ID: <20200211122323.GS8731@bombadil.infradead.org> (raw)
In-Reply-To: <20200211042536.GB242563@google.com>
On Mon, Feb 10, 2020 at 08:25:36PM -0800, Minchan Kim wrote:
> On Mon, Feb 10, 2020 at 07:54:12PM -0800, Matthew Wilcox wrote:
> > On Mon, Feb 10, 2020 at 07:50:04PM -0800, Minchan Kim wrote:
> > > On Mon, Feb 10, 2020 at 05:10:21PM -0800, Matthew Wilcox wrote:
> > > > On Mon, Feb 10, 2020 at 04:19:58PM -0800, Minchan Kim wrote:
> > > > > filemap_fault
> > > > > find a page form page(PG_uptodate|PG_readahead|PG_writeback)
> > > >
> > > > Uh ... That shouldn't be possible.
> > >
> > > Please see shrink_page_list. Vmscan uses PG_reclaim to accelerate
> > > page reclaim when the writeback is done so the page will have both
> > > flags at the same time and the PG reclaim could be regarded as
> > > PG_readahead in fault conext.
> >
> > What part of fault context can make that mistake? The snippet I quoted
> > below is from page_cache_async_readahead() where it will clearly not
> > make that mistake. There's a lot of code here; please don't presume I
> > know all the areas you're talking about.
>
> Sorry about being not clear. I am saying filemap_fault ->
> do_async_mmap_readahead
>
> Let's assume the page is hit in page cache and vmf->flags is !FAULT_FLAG
> TRIED so it calls do_async_mmap_readahead. Since the page has PG_reclaim
> and PG_writeback by shrink_page_list, it goes to
>
> do_async_mmap_readahead
> if (PageReadahead(page))
> fpin = maybe_unlock_mmap_for_io();
> page_cache_async_readahead
> if (PageWriteback(page))
> return;
> ClearPageReadahead(page); <- doesn't reach here until the writeback is clear
>
> So, mm_populate will repeat the loop until the writeback is done.
> It's my just theory but didn't comfirm it by the testing.
> If I miss something clear, let me know it.
Ah! Surely the right way to fix this is ...
+++ b/mm/filemap.c
@@ -2420,7 +2420,7 @@ static struct file *do_async_mmap_readahead(struct vm_fault *vmf,
return fpin;
if (ra->mmap_miss > 0)
ra->mmap_miss--;
- if (PageReadahead(page)) {
+ if (!PageWriteback(page) && PageReadahead(page)) {
fpin = maybe_unlock_mmap_for_io(vmf, fpin);
page_cache_async_readahead(mapping, ra, file,
page, offset, ra->ra_pages);
next prev parent reply other threads:[~2020-02-11 12:23 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 [this message]
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
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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