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Registered Address: Red Hat UK Ltd, Amberley Place, 107-111 Peascod Street, Windsor, Berkshire, SI4 1TE, United Kingdom. Registered in England and Wales under Company Registration No. 3798903 From: David Howells In-Reply-To: References: <163250387273.2330363.13240781819520072222.stgit@warthog.procyon.org.uk> <163250396319.2330363.10564506508011638258.stgit@warthog.procyon.org.uk> To: Matthew Wilcox Cc: dhowells@redhat.com, hch@lst.de, trond.myklebust@primarydata.com, Jens Axboe , "Darrick J. Wong" , linux-block@vger.kernel.org, linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, darrick.wong@oracle.com, viro@zeniv.linux.org.uk, jlayton@kernel.org, torvalds@linux-foundation.org, linux-nfs@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v3 9/9] mm: Remove swap BIO paths and only use DIO paths MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-ID: <2396105.1632584202.1@warthog.procyon.org.uk> Content-Transfer-Encoding: quoted-printable Date: Sat, 25 Sep 2021 16:36:42 +0100 Message-ID: <2396106.1632584202@warthog.procyon.org.uk> X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: AABCA5062840 X-Stat-Signature: f54bj6bdzpsks5qrxrta7ftmyyu5kh9y Authentication-Results: imf05.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=Zp3fL40T; spf=none (imf05.hostedemail.com: domain of dhowells@redhat.com has no SPF policy when checking 170.10.133.124) smtp.mailfrom=dhowells@redhat.com; dmarc=pass (policy=none) header.from=redhat.com X-HE-Tag: 1632584212-322977 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: Matthew Wilcox wrote: > On Fri, Sep 24, 2021 at 06:19:23PM +0100, David Howells wrote: > > Delete the BIO-generating swap read/write paths and always use ->swap_= rw(). > > This puts the mapping layer in the filesystem. > = > Is SWP_FS_OPS now unused after this patch? Ummm. Interesting question - it's only used in swap_set_page_dirty(): int swap_set_page_dirty(struct page *page) { struct swap_info_struct *sis =3D page_swap_info(page); if (data_race(sis->flags & SWP_FS_OPS)) { struct address_space *mapping =3D sis->swap_file->f_mapping; VM_BUG_ON_PAGE(!PageSwapCache(page), page); return mapping->a_ops->set_page_dirty(page); } else { return __set_page_dirty_no_writeback(page); } } > Also, do we still need ->swap_activate and ->swap_deactivate? f2fs does quite a lot of work in its ->swap_activate(), as does btrfs. I'= m not sure how necessary it is. cifs looks like it intends to use it, but i= t's not fully implemented yet. zonefs and nfs do some checking, including hol= e checking in nfs's case. nfs also does some setting up for the sunrpc transport. btrfs, cifs, f2fs and nfs all supply ->swap_deactivate() to undo the effec= ts of the activation. David