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Date:   Fri, 14 Aug 2020 02:43:55 +0100
From:   Matthew Wilcox <willy@infradead.org>
To:     Zhaoyang Huang <huangzhaoyang@gmail.com>
Cc:     Roman Gushchin <klamm@yandex-team.ru>,
        Andrew Morton <akpm@linux-foundation.org>,
        Zhaoyang Huang <zhaoyang.huang@unisoc.com>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH] mm : update ra->ra_pages if it's NOT equal to
 bdi->ra_pages
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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).