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Date:   Fri, 2 Dec 2022 11:22:45 +0100
From:   Christoph Hellwig <>
To:     "Ritesh Harjani (IBM)" <>
Cc:     Christoph Hellwig <>,
        Namjae Jeon <>,
        Sungjong Seo <>,
        Jan Kara <>,
        OGAWA Hirofumi <>,
        Mikulas Patocka <>,
        Dave Kleikamp <>,
        Bob Copeland <>,,,,,
Subject: Re: start removing writepage instances

On Thu, Nov 17, 2022 at 12:09:00AM +0530, Ritesh Harjani (IBM) wrote:
>    reclaim. Now IIUC from previous discussions [1][2][3], reclaims happens from
>    the tail end of the LRU list which could do an I/O of a single page while 
>    an ongoing writeback was in progress of multiple pages. This disrupts the I/O 
>    pattern to become more random in nature, compared to, if we would have let 
>    writeback/flusher do it's job of writing back dirty pages.


>    Also many filesystems behave very differently within their ->writepage calls,
>    e.g. ext4 doesn't actually write in ->writepage for DELAYED blocks.

I don't think it's many file systems.  As far as I can tell only ext4
actually is significantly different.

> 2. Now the other place from where ->writepage can be called from is, writeout()
>    function, which is a fallback function for migration (fallback_migrate_folio()).
>    fallback_migrate_folio() is called from move_to_new_folio() if ->migrate_folio 
>    is not defined for the FS.

Also there is generic_writepages and folio_write_one/write_one_page.

> Is above a correct understanding?


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