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Tue, 15 Nov 2022 01:22:41 +0100 (CET) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=codewreck.org; s=2; t=1668471766; bh=LIstCPb4xQT8VC3InWGVD6DG7uFdDJigM2d8zkWyzlg=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=vCzYdsKheoEw3SbPdq8dVompXvyIFPrTv8JxCFNOG8Sv6HDGCCc8EJ9TZ1mJpAJBP dfuVrLiLq6tLoPjg4vx7OnksEJRCe7+wk8srl2FEfVJUHcjtGwcL/HsmLnl7hxdJJO aAoNMpEDlxjtDi5MM90FWnau+y1nrDpmXPlLGgo+4TqQmnSnJRW9oMhrUC4NSrf2YI kwkv/XQ7cOL1UiwjAM4vHnFOYQEuzfy0wyv+LAwoyoMRSBGmD7j/7m8dWCIq6wXmGd HBU3jACL9WMITVf23xsnCvYbaZt3Cc3GmPhLK9M9qGkjB66Hluj/ez6JPYz8fB704q zmA+Da+v6VOiA== Received: from localhost (odin.codewreck.org [local]) by odin.codewreck.org (OpenSMTPD) with ESMTPA id 675ffca7; Tue, 15 Nov 2022 00:22:33 +0000 (UTC) Date: Tue, 15 Nov 2022 09:22:18 +0900 From: Dominique Martinet To: David Howells Cc: willy@infradead.org, dwysocha@redhat.com, Rohith Surabattula , Steve French , Shyam Prasad N , Ilya Dryomov , linux-cachefs@redhat.com, linux-cifs@vger.kernel.org, linux-afs@lists.infradead.org, v9fs-developer@lists.sourceforge.net, ceph-devel@vger.kernel.org, linux-nfs@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [RFC PATCH v2] mm, netfs, fscache: Stop read optimisation when folio removed from pagecache Message-ID: References: <166844174069.1124521.10890506360974169994.stgit@warthog.procyon.org.uk> MIME-Version: 1.0 Content-Type: text/plain; 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bh=LIstCPb4xQT8VC3InWGVD6DG7uFdDJigM2d8zkWyzlg=; b=E3FJbmfj2qN7YRV/Cbu5KsjiLIVAcu+Ey1+uhjWKNM6TAChcbW6XGwkB2uW96cs0uB2AKj V+RLg9gye3vUJz6C0n1xDb/B0nkyytIwksyWaXxB2yyTespmT6u0wn7OwBXYeYfe+rwrOl 9j9uA2p7C39S3cGqJfXm+Ab/25aSB2A= X-Rspam-User: Authentication-Results: imf26.hostedemail.com; dkim=pass header.d=codewreck.org header.s=2 header.b=G0AKICC0; dkim=pass header.d=codewreck.org header.s=2 header.b=vCzYdsKh; dmarc=pass (policy=none) header.from=codewreck.org; spf=pass (imf26.hostedemail.com: domain of asmadeus@codewreck.org designates 91.121.71.147 as permitted sender) smtp.mailfrom=asmadeus@codewreck.org X-Rspamd-Server: rspam02 X-Stat-Signature: xb36rfnrnwsuicpze9fzozkg5otsuif5 X-Rspamd-Queue-Id: BDC7B140005 X-HE-Tag: 1668471763-96088 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: David Howells wrote on Mon, Nov 14, 2022 at 04:02:20PM +0000: > Fscache has an optimisation by which reads from the cache are skipped until > we know that (a) there's data there to be read and (b) that data isn't > entirely covered by pages resident in the netfs pagecache. This is done > with two flags manipulated by fscache_note_page_release(): > > if (... > test_bit(FSCACHE_COOKIE_HAVE_DATA, &cookie->flags) && > test_bit(FSCACHE_COOKIE_NO_DATA_TO_READ, &cookie->flags)) > clear_bit(FSCACHE_COOKIE_NO_DATA_TO_READ, &cookie->flags); > > where the NO_DATA_TO_READ flag causes cachefiles_prepare_read() to indicate > that netfslib should download from the server or clear the page instead. > > The fscache_note_page_release() function is intended to be called from > ->releasepage() - but that only gets called if PG_private or PG_private_2 > is set - and currently the former is at the discretion of the network > filesystem and the latter is only set whilst a page is being written to the > cache, so sometimes we miss clearing the optimisation. > > Fix this by following Willy's suggestion[1] and adding an address_space > flag, AS_RELEASE_ALWAYS, that causes filemap_release_folio() to always call > ->release_folio() if it's set, even if PG_private or PG_private_2 aren't > set. Not familiar with the common code so just glanced at it and asked stupid questions. > diff --git a/fs/9p/cache.c b/fs/9p/cache.c > index cebba4eaa0b5..12c0ae29f185 100644 > --- a/fs/9p/cache.c > +++ b/fs/9p/cache.c > @@ -68,6 +68,8 @@ void v9fs_cache_inode_get_cookie(struct inode *inode) > &path, sizeof(path), > &version, sizeof(version), > i_size_read(&v9inode->netfs.inode)); > + if (v9inode->netfs.cache) > + mapping_set_release_always(inode->i_mapping); > > p9_debug(P9_DEBUG_FSC, "inode %p get cookie %p\n", > inode, v9fs_inode_cookie(v9inode)); > diff --git a/fs/9p/vfs_inode.c b/fs/9p/vfs_inode.c > index 4d1a4a8d9277..b553fe3484c1 100644 > --- a/fs/9p/vfs_inode.c > +++ b/fs/9p/vfs_inode.c > @@ -394,6 +394,7 @@ void v9fs_evict_inode(struct inode *inode) > version = cpu_to_le32(v9inode->qid.version); > fscache_clear_inode_writeback(v9fs_inode_cookie(v9inode), inode, > &version); > + mapping_clear_release_always(inode->i_mapping); any harm in setting this if netfs isn't enabled? (just asking because you checked in fs/9p/cache.c above) > clear_inode(inode); > filemap_fdatawrite(&inode->i_data); > > diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h > index bbccb4044222..3db9a6225bc0 100644 > --- a/include/linux/pagemap.h > +++ b/include/linux/pagemap.h > @@ -199,6 +199,7 @@ enum mapping_flags { > /* writeback related tags are not used */ > AS_NO_WRITEBACK_TAGS = 5, > AS_LARGE_FOLIO_SUPPORT = 6, > + AS_RELEASE_ALWAYS, /* Call ->release_folio(), even if no private data */ > }; > > /** > @@ -269,6 +270,21 @@ static inline int mapping_use_writeback_tags(struct address_space *mapping) > return !test_bit(AS_NO_WRITEBACK_TAGS, &mapping->flags); > } > > +static inline bool mapping_release_always(const struct address_space *mapping) > +{ > + return test_bit(AS_RELEASE_ALWAYS, &mapping->flags); > +} > + > +static inline void mapping_set_release_always(struct address_space *mapping) > +{ > + set_bit(AS_RELEASE_ALWAYS, &mapping->flags); > +} > + > +static inline void mapping_clear_release_always(struct address_space *mapping) > +{ > + set_bit(AS_RELEASE_ALWAYS, &mapping->flags); clear_bit certainly? > +} > + > static inline gfp_t mapping_gfp_mask(struct address_space * mapping) > { > return mapping->gfp_mask; > diff --git a/mm/truncate.c b/mm/truncate.c > index c0be77e5c008..0d4dd233f518 100644 > --- a/mm/truncate.c > +++ b/mm/truncate.c > @@ -19,7 +19,6 @@ > #include > #include > #include > -#include /* grr. try_to_release_page */ > #include > #include > #include "internal.h" > @@ -276,7 +275,7 @@ static long mapping_evict_folio(struct address_space *mapping, > if (folio_ref_count(folio) > > folio_nr_pages(folio) + folio_has_private(folio) + 1) > return 0; > - if (folio_has_private(folio) && !filemap_release_folio(folio, 0)) > + if (!filemap_release_folio(folio, 0)) should this (and all others) check for folio_needs_release instead of has_private? filemap_release_folio doesn't check as far as I can see, but perhaps it's already fast and noop for another reason I didn't see. > return 0; > > return remove_mapping(mapping, folio); -- Dominique