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From:   "NeilBrown" <neilb@suse.de>
To:     "Matthew Wilcox" <willy@infradead.org>
Cc:     "Andrew Morton" <akpm@linux-foundation.org>,
        "Mel Gorman" <mgorman@suse.de>,
        "Philipp Reisner" <philipp.reisner@linbit.com>,
        "Lars Ellenberg" <lars.ellenberg@linbit.com>,
        "Jan Kara" <jack@suse.com>,
        "Ryusuke Konishi" <konishi.ryusuke@gmail.com>,
        "Darrick J. Wong" <djwong@kernel.org>, linux-xfs@vger.kernel.org,
        linux-ext4@vger.kernel.org, linux-nilfs@vger.kernel.org,
        linux-mm@kvack.org, linux-fsdevel@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/2] Remove inode_congested()
In-reply-to: <YbbKjjFzIzSBJWCn@casper.infradead.org>
References: <163936868317.23860.5037433897004720387.stgit@noble.brown>,
 <163936886725.23860.2403757518009677424.stgit@noble.brown>,
 <YbbKjjFzIzSBJWCn@casper.infradead.org>
Date:   Mon, 13 Dec 2021 15:59:30 +1100
Message-id: <163937157093.22433.10907067066589299028@noble.neil.brown.name>
Precedence: bulk

On Mon, 13 Dec 2021, Matthew Wilcox wrote:
> On Mon, Dec 13, 2021 at 03:14:27PM +1100, NeilBrown wrote:
> > diff --git a/mm/vmscan.c b/mm/vmscan.c
> > index fb9584641ac7..540aa0ea67ff 100644
> > --- a/mm/vmscan.c
> > +++ b/mm/vmscan.c
> > @@ -989,17 +989,6 @@ static inline int is_page_cache_freeable(struct page=
 *page)
> >  	return page_count(page) - page_has_private(page) =3D=3D 1 + page_cache_=
pins;
> >  }
> > =20
> > -static int may_write_to_inode(struct inode *inode)
> > -{
> > -	if (current->flags & PF_SWAPWRITE)
> > -		return 1;
> > -	if (!inode_write_congested(inode))
> > -		return 1;
> > -	if (inode_to_bdi(inode) =3D=3D current->backing_dev_info)
> > -		return 1;
> > -	return 0;
> > -}
>=20
> Why is it safe to get rid of the PF_SWAPWRITE and current->backing_dev_info
> checks?

Ask George Bool.
If inode_write_congested() returns False, then may_write_to_inode() will
always return True.

NeilBrown


>=20
> > @@ -1158,8 +1147,6 @@ static pageout_t pageout(struct page *page, struct =
address_space *mapping)
> >  	}
> >  	if (mapping->a_ops->writepage =3D=3D NULL)
> >  		return PAGE_ACTIVATE;
> > -	if (!may_write_to_inode(mapping->host))
> > -		return PAGE_KEEP;
> > =20
> >  	if (clear_page_dirty_for_io(page)) {
> >  		int res;
>=20
>=20