linux-kernel - Re: [RFC PATCH] mm: fadvise: avoid fadvise for fs without backing device

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Message-ID: <CALvZod5nvGtHAduA89Ak5gOofJVMA7bhmXjRrjseTptoqz+cmA@mail.gmail.com>
Date:   Fri, 25 Aug 2017 17:22:58 -0700
From:   Shakeel Butt <shakeelb@...gle.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Mel Gorman <mgorman@...e.de>, Johannes Weiner <hannes@...xchg.org>,
        Hillf Danton <hillf.zj@...baba-inc.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Hugh Dickins <hughd@...gle.com>,
        Greg Thelen <gthelen@...gle.com>,
        Linux MM <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH] mm: fadvise: avoid fadvise for fs without backing device

On Fri, Aug 25, 2017 at 2:49 PM, Andrew Morton
<akpm@...ux-foundation.org> wrote:
> On Thu, 17 Aug 2017 18:20:17 -0700 Shakeel Butt <shakeelb@...gle.com> wrote:
>
>> +linux-mm, linux-kernel
>>
>> On Thu, Aug 17, 2017 at 6:10 PM, Shakeel Butt <shakeelb@...gle.com> wrote:
>> > The fadvise() manpage is silent on fadvise()'s effect on
>> > memory-based filesystems (shmem, hugetlbfs & ramfs) and pseudo
>> > file systems (procfs, sysfs, kernfs). The current implementaion
>> > of fadvise is mostly a noop for such filesystems except for
>> > FADV_DONTNEED which will trigger expensive remote LRU cache
>> > draining. This patch makes the noop of fadvise() on such file
>> > systems very explicit.
>> >
>> > However this change has two side effects for ramfs and one for
>> > tmpfs. First fadvise(FADV_DONTNEED) can remove the unmapped clean
>> > zero'ed pages of ramfs (allocated through read, readahead & read
>> > fault) and tmpfs (allocated through read fault). Also
>> > fadvise(FADV_WILLNEED) on create such clean zero'ed pages for
>> > ramfs.
>
> That sentence makes no sense.  I assume "fadvise(FADV_WILLNEED) will
> create"?
>

Sorry about that, it should be "fadvise(FADV_WILLNEED) can create".

>