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Message-ID: <20221202102245.GA17715@lst.de>
Date: Fri, 2 Dec 2022 11:22:45 +0100
From: Christoph Hellwig <hch@....de>
To: "Ritesh Harjani (IBM)" <ritesh.list@...il.com>
Cc: Christoph Hellwig <hch@....de>,
Namjae Jeon <linkinjeon@...nel.org>,
Sungjong Seo <sj1557.seo@...sung.com>,
Jan Kara <jack@...e.com>,
OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>,
Mikulas Patocka <mikulas@...ax.karlin.mff.cuni.cz>,
Dave Kleikamp <shaggy@...nel.org>,
Bob Copeland <me@...copeland.com>,
linux-fsdevel@...r.kernel.org, linux-ext4@...r.kernel.org,
jfs-discussion@...ts.sourceforge.net,
linux-karma-devel@...ts.sourceforge.net, linux-mm@...ck.org
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.
Yes.
> 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?
Yes.
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