From: Michal Hocko <mhocko@kernel.org>
To: Johannes Weiner <hannes@cmpxchg.org>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Mel Gorman <mgorman@suse.de>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
kernel-team@fb.com
Subject: Re: [PATCH 4/5] mm: vmscan: only write dirty pages that the scanner has seen twice
Date: Thu, 26 Jan 2017 14:29:23 +0100 [thread overview]
Message-ID: <20170126132922.GD7827@dhcp22.suse.cz> (raw)
In-Reply-To: <20170123181641.23938-5-hannes@cmpxchg.org>
On Mon 23-01-17 13:16:40, Johannes Weiner wrote:
> Dirty pages can easily reach the end of the LRU while there are still
> clean pages to reclaim around. Don't let kswapd write them back just
> because there are a lot of them. It costs more CPU to find the clean
> pages, but that's almost certainly better than to disrupt writeback
> from the flushers with LRU-order single-page writes from reclaim. And
> the flushers have been woken up by that point, so we spend IO capacity
> on flushing and CPU capacity on finding the clean cache.
>
> Only start writing dirty pages if they have cycled around the LRU
> twice now and STILL haven't been queued on the IO device. It's
> possible that the dirty pages are so sparsely distributed across
> different bdis, inodes, memory cgroups, that the flushers take forever
> to get to the ones we want reclaimed. Once we see them twice on the
> LRU, we know that's the quicker way to find them, so do LRU writeback.
>
> Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Michal Hocko <mhocko@suse.com>
> ---
> mm/vmscan.c | 15 ++++++++++-----
> 1 file changed, 10 insertions(+), 5 deletions(-)
>
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 915fc658de41..df0fe0cc438e 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -1153,13 +1153,18 @@ static unsigned long shrink_page_list(struct list_head *page_list,
>
> if (PageDirty(page)) {
> /*
> - * Only kswapd can writeback filesystem pages to
> - * avoid risk of stack overflow but only writeback
> - * if many dirty pages have been encountered.
> + * Only kswapd can writeback filesystem pages
> + * to avoid risk of stack overflow. But avoid
> + * injecting inefficient single-page IO into
> + * flusher writeback as much as possible: only
> + * write pages when we've encountered many
> + * dirty pages, and when we've already scanned
> + * the rest of the LRU for clean pages and see
> + * the same dirty pages again (PageReclaim).
> */
> if (page_is_file_cache(page) &&
> - (!current_is_kswapd() ||
> - !test_bit(PGDAT_DIRTY, &pgdat->flags))) {
> + (!current_is_kswapd() || !PageReclaim(page) ||
> + !test_bit(PGDAT_DIRTY, &pgdat->flags))) {
> /*
> * Immediately reclaim when written back.
> * Similar in principal to deactivate_page()
> --
> 2.11.0
>
> --
> To unsubscribe, send a message with 'unsubscribe linux-mm' in
> the body to majordomo@kvack.org. For more info on Linux MM,
> see: http://www.linux-mm.org/ .
> Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
--
Michal Hocko
SUSE Labs
next prev parent reply other threads:[~2017-01-26 13:29 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-01-23 18:16 [PATCH 0/5] mm: vmscan: fix kswapd writeback regression Johannes Weiner
2017-01-23 18:16 ` [PATCH 1/5] mm: vmscan: scan dirty pages even in laptop mode Johannes Weiner
2017-01-26 1:27 ` Minchan Kim
2017-01-26 9:52 ` Mel Gorman
2017-01-26 13:13 ` Michal Hocko
2017-01-23 18:16 ` [PATCH 2/5] mm: vmscan: kick flushers when we encounter dirty pages on the LRU Johannes Weiner
2017-01-26 1:35 ` Minchan Kim
2017-01-26 9:57 ` Mel Gorman
2017-01-26 17:47 ` Johannes Weiner
2017-01-26 18:47 ` Mel Gorman
2017-01-26 13:16 ` Michal Hocko
2017-01-23 18:16 ` [PATCH 3/5] mm: vmscan: remove old flusher wakeup from direct reclaim path Johannes Weiner
2017-01-26 1:38 ` Minchan Kim
2017-01-26 10:05 ` Mel Gorman
2017-01-26 18:50 ` Johannes Weiner
2017-01-26 20:45 ` Mel Gorman
2017-01-27 12:01 ` Michal Hocko
2017-01-27 14:27 ` Mel Gorman
2017-01-26 13:21 ` Michal Hocko
2017-01-23 18:16 ` [PATCH 4/5] mm: vmscan: only write dirty pages that the scanner has seen twice Johannes Weiner
2017-01-26 1:42 ` Minchan Kim
2017-01-26 10:08 ` Mel Gorman
2017-01-26 13:29 ` Michal Hocko [this message]
2017-01-23 18:16 ` [PATCH 5/5] mm: vmscan: move dirty pages out of the way until they're flushed Johannes Weiner
2017-01-26 1:47 ` Minchan Kim
2017-01-26 10:19 ` Mel Gorman
2017-01-26 20:07 ` Johannes Weiner
2017-01-26 20:58 ` Mel Gorman
2017-01-26 13:52 ` Michal Hocko
2017-01-26 5:44 ` [PATCH 0/5] mm: vmscan: fix kswapd writeback regression Hillf Danton
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