linux-kernel - Re: [PATCH v3] btrfs: implement migratepage callback

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Message-ID: <20200311013029.GE96999@carbon.dhcp.thefacebook.com>
Date:   Tue, 10 Mar 2020 18:30:29 -0700
From:   Roman Gushchin <guro@...com>
To:     <dsterba@...e.cz>, Josef Bacik <josef@...icpanda.com>,
        Chris Mason <clm@...com>, David Sterba <dsterba@...e.com>,
        <linux-btrfs@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <kernel-team@...com>, Rik van Riel <riel@...riel.com>
Subject: Re: [PATCH v3] btrfs: implement migratepage callback

On Wed, Mar 11, 2020 at 01:40:12AM +0100, David Sterba wrote:
> On Wed, Mar 04, 2020 at 04:57:35PM -0800, Roman Gushchin wrote:
> > Currently btrfs doesn't provide a migratepage callback. It means that
> > fallback_migrate_page()	is used to migrate btrfs pages.
> 
> The callback exists for the metadata pages (btree_migratepage), so I've
> added 'for data pages' where appropriate.

Agree.

> 
> > fallback_migrate_page() cannot move dirty pages, instead it tries to
> > flush them (in sync mode) or just fails (in async mode).
> > 
> > In the sync mode pages which are scheduled to be processed by
> > btrfs_writepage_fixup_worker() can't be effectively flushed by the
> > migration code, because there is no established way to wait for the
> > completion of the delayed work.
> > 
> > It all leads to page migration failures.
> > 
> > To fix it the patch implements a btrs-specific migratepage callback,
> > which is similar to iomap_migrate_page() used by some other fs, except
> > it does take care of the PagePrivate2 flag which is used for data
> > ordering purposes.
> > 
> > v3: fixed the build issue once again
> > v2: fixed the build issue found by the kbuild test robot <lkp@...el.com>
> > 
> > Signed-off-by: Roman Gushchin <guro@...com>
> > Reviewed-by: Chris Mason <clm@...com>
> 
> Added to devel queue, thanks.

Thank you!

Roman