linux-kernel - Re: [PATCH -next] mm/filemap: fix that first page is not mark accessed in filemap

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Message-ID: <YpkB1+PwIZ3AKUqg@casper.infradead.org>
Date:   Thu, 2 Jun 2022 19:30:47 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     Yu Kuai <yukuai3@...wei.com>
Cc:     akpm@...ux-foundation.org, kent.overstreet@...il.com,
        axboe@...nel.dk, linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, yi.zhang@...wei.com
Subject: Re: [PATCH -next] mm/filemap: fix that first page is not mark
 accessed in filemap_read()

On Thu, Jun 02, 2022 at 04:21:29PM +0800, Yu Kuai wrote:
> In filemap_read(), 'ra->prev_pos' is set to 'iocb->ki_pos + copied',
> while it should be 'iocb->ki_ops'.

Can you walk me through your reasoning which leads you to believe that
it should be ki_pos instead of ki_pos + copied?  As I understand it,
prev_pos is the end of the previous read, not the beginning of the
previous read.

For consequence,
> folio_mark_accessed() will not be called for 'fbatch.folios[0]' since
> 'iocb->ki_pos' is always equal to 'ra->prev_pos'.

I don't follow this, but maybe I'm just being slow.