From: Minchan Kim <minchan@kernel.org>
To: Jaewon Kim <jaewon31.kim@samsung.com>,
Johannes Weiner <hannes@cmpxchg.org>
Cc: mgorman@suse.de, m.szyprowski@samsung.com, mina86@mina86.com,
riel@redhat.com, akpm@linux-foundation.org, linux-mm@kvack.org,
linux-kernel@vger.kernel.org, jaewon31.kim@gmail.com,
ytk.lee@samsung.com
Subject: Re: [PATCH] mm/vmscan: skip layzfree page on reclaim_clean_pages_from_list
Date: Thu, 16 Apr 2020 17:38:37 -0700 [thread overview]
Message-ID: <20200417003837.GA90471@google.com> (raw)
In-Reply-To: <20200416033514.6366-1-jaewon31.kim@samsung.com>
Hi Jaewon,
On Thu, Apr 16, 2020 at 12:35:14PM +0900, Jaewon Kim wrote:
> This patch fix nr_isolate_* mismatch problem between cma and dirty
> lazyfree page.
>
> If try_to_unmap_one is used for reclaim and it detects a dirty lazyfree
> page, then the lazyfree page is changed to a normal anon page having
> SwapBacked by commit 18863d3a3f59 ("mm: remove SWAP_DIRTY in ttu"). Even
> with the change, reclaim context correctly counts isolated files because
> it uses is_file_lru to distinguish file. And the change to anon is not
> happened if try_to_unmap_one is used for migration. So migration context
> like compaction also correctly counts isolated files even though it uses
> page_is_file_lru insted of is_file_lru. Recently page_is_file_cache was
> renamed to page_is_file_lru by commit 9de4f22a60f7 ("mm: code cleanup for
> MADV_FREE").
>
> But the nr_isolate_* mismatch problem happens on cma alloc. There is
> reclaim_clean_pages_from_list which is being used only by cma. It was
> introduced by commit 02c6de8d757c ("mm: cma: discard clean pages during
> contiguous allocation instead of migration") to reclaim clean file pages
> without migration. The cma alloc uses both reclaim_clean_pages_from_list
> and migrate_pages, and it uses page_is_file_lru to count isolated
> files. If there are dirty lazyfree pages allocated from cma memory
> region, the pages are counted as isolated file at the beginging but are
> counted as isolated anon after finished.
>
> Mem-Info:
> Node 0 active_anon:3045904kB inactive_anon:611448kB active_file:14892kB inactive_file:205636kB unevictable:10416kB isolated(anon):0kB isolated(file):37664kB mapped:630216kB dirty:384kB writeback:0kB shmem:42576kB writeback_tmp:0kB unstable:0kB all_unreclaimable? no
>
> Like log above, there was too much isolated file, 37664kB, which
> triggers too_many_isolated in reclaim when there is no isolated file in
> system wide. It could be reproducible by running two programs, doing
> MADV_FREE, writing and doing cma alloc, respectively. Although isolated
> anon is 0, I found that the internal value of isolated anon was the
> negative value of isolated file.
>
> Fix this by skipping anon pages on reclaim_clean_pages_from_list. The
> lazyfree page can be checked by both PageAnon(page) and
> page_is_file_lru. But in this case, PageAnon is enough to skip all
> anon pages.
>
> Reported-by: Yong-Taek Lee <ytk.lee@samsung.com>
> Signed-off-by: Jaewon Kim <jaewon31.kim@samsung.com>
Thanks for the investigation!
The thing is MADV_FREEed page since supporting swapless could change
his LRU status between reclaim.
I am worry about voiding the optimization we have kept in CMA but
also don't have good idea, either so I tend to agree with this.
Let me Cc Johannes who might have better idea.
> ---
> mm/vmscan.c | 3 +++
> 1 file changed, 3 insertions(+)
>
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index b06868fc4926..9380a18eef5e 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -1497,6 +1497,9 @@ unsigned long reclaim_clean_pages_from_list(struct zone *zone,
> LIST_HEAD(clean_pages);
>
> list_for_each_entry_safe(page, next, page_list, lru) {
> + /* to avoid race with MADV_FREE anon page */
> + if (PageAnon(page))
> + continue;
> if (page_is_file_lru(page) && !PageDirty(page) &&
> !__PageMovable(page) && !PageUnevictable(page)) {
> ClearPageActive(page);
> --
> 2.13.7
>
next prev parent reply other threads:[~2020-04-17 0:38 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <CGME20200416033543epcas1p2b256bef770bb1310a9bf62bda80a976a@epcas1p2.samsung.com>
2020-04-16 3:35 ` [PATCH] mm/vmscan: skip layzfree page on reclaim_clean_pages_from_list Jaewon Kim
2020-04-16 5:17 ` Jaewon Kim
2020-04-17 0:38 ` Minchan Kim [this message]
2020-04-17 15:13 ` Minchan Kim
2020-04-17 23:45 ` Jaewon Kim
2020-04-20 6:19 ` Jaewon Kim
2020-04-21 12:06 ` Jaewon Kim
2020-04-22 5:40 ` Minchan Kim
2020-04-22 8:39 ` Jaewon Kim
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