linux-kernel - Re: [PATCH] mm : update ra->ra_pages if it's NOT equal to bdi->ra

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Date:   Fri, 14 Aug 2020 03:07:00 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     Zhaoyang Huang <huangzhaoyang@...il.com>
Cc:     Roman Gushchin <klamm@...dex-team.ru>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Zhaoyang Huang <zhaoyang.huang@...soc.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm : update ra->ra_pages if it's NOT equal to
 bdi->ra_pages

On Fri, Aug 14, 2020 at 02:43:55AM +0100, Matthew Wilcox wrote:
> On Fri, Aug 14, 2020 at 09:30:11AM +0800, Zhaoyang Huang wrote:
> > file->f_ra->ra_pages will remain the initialized value since it opend, which may
> > be NOT equal to bdi->ra_pages as the latter one is updated somehow(etc,
> > echo xxx > /sys/block/dm/queue/read_ahead_kb).So sync ra->ra_pages to the
> > updated value when sync read.
> 
> It still ignores the work done by shrink_readahead_size_eio()
> and fadvise(POSIX_FADV_SEQUENTIAL).

... by the way, if you're trying to update one particular file's readahead
state, you can just call fadvise(POSIX_FADV_NORMAL) on it.

If you want to update every open file's ra_pages by writing to sysfs,
then just no.  We don't do that.

You haven't said what problem you're facing, so I really can't be more
helpful.