From: Andrew Morton <akpm@linux-foundation.org>
To: Minchan Kim <minchan@kernel.org>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org,
Mel Gorman <mgorman@suse.de>, Rik van Riel <riel@redhat.com>,
Hugh Dickins <hughd@google.com>,
Johannes Weiner <hannes@cmpxchg.org>,
Michal Hocko <mhocko@suse.cz>
Subject: Re: [PATCH v3 0/3] free reclaimed pages by paging out instantly
Date: Wed, 2 Jul 2014 13:42:15 -0700 [thread overview]
Message-ID: <20140702134215.2bf830dcb904c34bd2e2b9e8@linux-foundation.org> (raw)
In-Reply-To: <1404260029-11525-1-git-send-email-minchan@kernel.org>
On Wed, 2 Jul 2014 09:13:46 +0900 Minchan Kim <minchan@kernel.org> wrote:
> Normally, I/O completed pages for reclaim would be rotated into
> inactive LRU tail without freeing. The why it works is we can't free
> page from atomic context(ie, end_page_writeback) due to vaious locks
> isn't aware of atomic context.
>
> So for reclaiming the I/O completed pages, we need one more iteration
> of reclaim and it could make unnecessary aging as well as CPU overhead.
>
> Long time ago, at the first trial, most concern was memcg locking
> but recently, Johnannes tried amazing effort to make memcg lock simple
> and got merged into mmotm so I coded up based on mmotm tree.
> (Kudos to Johannes)
>
> On 1G, 12 CPU kvm guest, build kernel 5 times and result was
>
> allocstall
> vanilla: records: 5 avg: 4733.80 std: 913.55(19.30%) max: 6442.00 min: 3719.00
> improve: records: 5 avg: 1514.20 std: 441.69(29.17%) max: 1974.00 min: 863.00
Well yes. We're now doing unaccounted, impact-a-random-process work in
irq context which was previously being done in process context,
accounted to the process which was allocating the memory. Some would
call this a regression ;)
> pgrotated
> vanilla: records: 5 avg: 873313.80 std: 40999.20(4.69%) max: 954722.00 min: 845903.00
> improve: records: 5 avg: 28406.40 std: 3296.02(11.60%) max: 34552.00 min: 25047.00
Still a surprisingly high amount of rotation going on.
> Most of field in vmstat are not changed too much but things I can notice
> is allocstall and pgrotated. We could save allocstall(ie, direct relcaim)
> and pgrotated very much.
>
> Welcome testing, review and any feedback!
Well, it will worsen IRQ latencies and it's all more code for us to
maintain. I think I'd like to see a better story about the end-user
benefits before proceeding.
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next prev parent reply other threads:[~2014-07-02 20:42 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-07-02 0:13 Minchan Kim
2014-07-02 0:13 ` [PATCH v3 1/3] mm: Don't hide spin_lock in swap_info_get internal Minchan Kim
2014-07-02 0:13 ` [PATCH v3 2/3] mm: Introduce atomic_remove_mapping Minchan Kim
2014-07-02 0:13 ` [PATCH v3 3/3] mm: Free reclaimed pages indepdent of next reclaim Minchan Kim
2014-07-02 20:42 ` Andrew Morton [this message]
2014-07-03 0:59 ` [PATCH v3 0/3] free reclaimed pages by paging out instantly Minchan Kim
2014-07-07 19:13 ` Andrew Morton
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