linux-kernel - Re: [PATCH] writeback: Account the number of pages written back

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Message-Id: <20230702130615.b72616d7f03b3ab4f6fc8dab@linux-foundation.org>
Date:   Sun, 2 Jul 2023 13:06:15 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     "Matthew Wilcox (Oracle)" <willy@...radead.org>
Cc:     linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Jan Kara <jack@...e.cz>,
        Christoph Hellwig <hch@....de>
Subject: Re: [PATCH] writeback: Account the number of pages written back

On Wed, 28 Jun 2023 19:55:48 +0100 "Matthew Wilcox (Oracle)" <willy@...radead.org> wrote:

> nr_to_write is a count of pages, so we need to decrease it by the number
> of pages in the folio we just wrote, not by 1.  Most callers specify
> either LONG_MAX or 1, so are unaffected, but writeback_sb_inodes()
> might end up writing 512x as many pages as it asked for.

512 is a big number,  Should we backport this?

> Fixes: 793917d997df ("mm/readahead: Add large folio readahead")

I'm not seeing how a readahead change messed up writeback accounting?