From: Andrew Morton <akpm@linux-foundation.org>
To: Minchan Kim <minchan@kernel.org>
Cc: "Huang, Ying" <ying.huang@intel.com>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
Johannes Weiner <hannes@cmpxchg.org>,
Rik van Riel <riel@redhat.com>, Shaohua Li <shli@kernel.org>,
Hugh Dickins <hughd@google.com>,
Fengguang Wu <fengguang.wu@intel.com>,
Tim Chen <tim.c.chen@intel.com>,
Dave Hansen <dave.hansen@intel.com>
Subject: Re: [PATCH -mm -v4 3/5] mm, swap: VMA based swap readahead
Date: Wed, 13 Sep 2017 14:02:29 -0700 [thread overview]
Message-ID: <20170913140229.8a6cad6f017fa3ea8b53cefc@linux-foundation.org> (raw)
In-Reply-To: <20170913014019.GB29422@bbox>
On Wed, 13 Sep 2017 10:40:19 +0900 Minchan Kim <minchan@kernel.org> wrote:
> Every zram users like low-end android device has used 0 page-cluster
> to disable swap readahead because it has no seek cost and works as
> synchronous IO operation so if we do readahead multiple pages,
> swap falut latency would be (4K * readahead window size). IOW,
> readahead is meaningful only if it doesn't bother faulted page's
> latency.
>
> However, this patch introduces additional knob /sys/kernel/mm/swap/
> vma_ra_max_order as well as page-cluster. It means existing users
> has used disabled swap readahead doesn't work until they should be
> aware of new knob and modification of their script/code to disable
> vma_ra_max_order as well as page-cluster.
>
> I say it's a *regression* and wanted to fix it but Huang's opinion
> is that it's not a functional regression so userspace should be fixed
> by themselves.
> Please look into detail of discussion in
> http://lkml.kernel.org/r/%3C1505183833-4739-4-git-send-email-minchan@kernel.org%3E
hm, tricky problem. I do agree that linking the physical and virtual
readahead schemes in the proposed fashion is unfortunate. I also agree
that breaking existing setups (a bit) is also unfortunate.
Would it help if, when page-cluster is written to zero, we do
printk_once("physical readahead disabled, virtual readahead still
enabled. Disable virtual readhead via
/sys/kernel/mm/swap/vma_ra_max_order").
Or something like that. It's pretty lame, but it should help alert the
zram-readahead-disabling people to the issue?
next prev parent reply other threads:[~2017-09-13 21:02 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-08-07 5:40 [PATCH -mm -v4 0/5] mm, swap: VMA based swap readahead Huang, Ying
2017-08-07 5:40 ` [PATCH -mm -v4 1/5] mm, swap: Add swap readahead hit statistics Huang, Ying
2017-08-09 21:50 ` Andrew Morton
2017-08-09 23:17 ` Huang, Ying
2017-08-07 5:40 ` [PATCH -mm -v4 2/5] mm, swap: Fix swap readahead marking Huang, Ying
2017-08-07 5:40 ` [PATCH -mm -v4 3/5] mm, swap: VMA based swap readahead Huang, Ying
2017-09-13 1:40 ` Minchan Kim
2017-09-13 21:02 ` Andrew Morton [this message]
2017-09-14 0:53 ` Huang, Ying
2017-09-14 8:15 ` Minchan Kim
2017-09-14 7:53 ` Minchan Kim
2017-09-14 12:01 ` Huang, Ying
2017-09-14 13:14 ` Minchan Kim
2017-09-14 21:21 ` Andrew Morton
2017-09-15 3:15 ` Huang, Ying
2017-09-15 3:42 ` Minchan Kim
2017-09-15 4:46 ` Huang, Ying
2017-08-07 5:40 ` [PATCH -mm -v4 4/5] mm, swap: Add sysfs interface for " Huang, Ying
2017-08-07 5:40 ` [PATCH -mm -v4 5/5] mm, swap: Don't use VMA based swap readahead if HDD is used as swap Huang, Ying
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