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Sun, 26 Sep 2021 16:08:57 -0700 (PDT) Received: from [10.89.85.1] (c02drav6md6t.dhcp.fujisawa.hgst.com [10.89.85.1]) by usg-ed-osssrv.wdc.com (Postfix) with ESMTPSA id 4HHhKL6dDzz1RvTg; Sun, 26 Sep 2021 16:08:54 -0700 (PDT) Message-ID: <5fde9167-6f8b-c698-f34d-d7fafd4219f7@opensource.wdc.com> Date: Mon, 27 Sep 2021 08:08:53 +0900 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:91.0) Gecko/20100101 Thunderbird/91.1.1 Subject: Re: [PATCH v3 9/9] mm: Remove swap BIO paths and only use DIO paths Content-Language: en-US To: Matthew Wilcox , David Howells Cc: 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 References: <163250387273.2330363.13240781819520072222.stgit@warthog.procyon.org.uk> <163250396319.2330363.10564506508011638258.stgit@warthog.procyon.org.uk> <2396106.1632584202@warthog.procyon.org.uk> From: Damien Le Moal Organization: Western Digital In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: A20FCD032041 X-Stat-Signature: k5qku5z863id1smmp76yao4j43i11n7s Authentication-Results: imf21.hostedemail.com; dkim=pass header.d=wdc.com header.s=dkim.wdc.com header.b=nsf8jCh2; dkim=pass header.d=opensource.wdc.com header.s=dkim header.b=TmqmtvnU; dmarc=pass (policy=quarantine) header.from=opensource.wdc.com; spf=pass (imf21.hostedemail.com: domain of "prvs=896124dd8=damien.lemoal@opensource.wdc.com" designates 216.71.153.141 as permitted sender) smtp.mailfrom="prvs=896124dd8=damien.lemoal@opensource.wdc.com" X-HE-Tag: 1632697743-63598 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: On 2021/09/26 2:09, Matthew Wilcox wrote: > On Sat, Sep 25, 2021 at 04:36:42PM +0100, David Howells wrote: >> 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 = page_swap_info(page); >> >> if (data_race(sis->flags & SWP_FS_OPS)) { >> struct address_space *mapping = 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); >> } >> } > > I suspect that's no longer necessary. NFS was the only filesystem > using SWP_FS_OPS and ... > > fs/nfs/file.c: .set_page_dirty = __set_page_dirty_nobuffers, > > so it's not like NFS does anything special to reserve memory to write > back swap pages. > >>> 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 it's >> not fully implemented yet. zonefs and nfs do some checking, including hole >> 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 effects >> of the activation. > > Right ... so my question really is, now that we're doing I/O through > aops->direct_IO (or ->swap_rw), do those magic things need to be done? > After all, open(O_DIRECT) doesn't do these same magic things. They're > really there to allow the direct-to-BIO path to work, and you're removing > that here. For zonefs, ->swap_activate() checks that the user is not trying to use a sequential write only file for swap. Swap cannot work on these files as there are no guarantees that the writes will be sequential. -- Damien Le Moal Western Digital Research