linux-kernel - Re: [PATCH] mm : sync ra->ra_pages with bdi->ra

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Message-ID: <20200814114819.GW17456@casper.infradead.org>
Date:   Fri, 14 Aug 2020 12:48:19 +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 : sync ra->ra_pages with bdi->ra_pages

On Fri, Aug 14, 2020 at 05:03:44PM +0800, Zhaoyang Huang wrote:
> Some system(like android) will turbo read during startup via expanding the
> readahead window and then set it back to normal(128kb as usual). However, some
> files in the system process context will keep to be opened since it is opened
> up and has no chance to sync with the updated value as it is almost impossible
> to change the files attached to the inode(processes are unaware of these things)

Hang on, you're saying that the _only_ way to do turbo-read is the way
that userspace currently does it, and userspace cannot be modified,
only the kernel?  I think somebody has their priorities wrong!

> We sync ra->ra_pages with bdi->ra_pages when read. Furthermore, in consideration
> of the scenario of eio and fadvise(...,POSIX_FADV_SEQUENTIAL).We introduce a
> seq_read_fact to record the factors of above two cases.

No, this is far too complicated.