From patchwork Fri Oct 22 19:05:08 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: David Howells X-Patchwork-Id: 12578781 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id F4113C433F5 for ; Fri, 22 Oct 2021 19:05:37 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D96E461038 for ; Fri, 22 Oct 2021 19:05:37 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233615AbhJVTHy (ORCPT ); Fri, 22 Oct 2021 15:07:54 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:39480 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234059AbhJVTHo (ORCPT ); Fri, 22 Oct 2021 15:07:44 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1634929525; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=VjuM0Z1Ol4Mfqz9YrQA7/+R9GNqZnkOBaFnc7EjRc70=; b=CVRGEGLk8XRRHH8ttxzayGFoesrH/tHnFS8lAFcdVur5agtq6Zjc54xCNnLnITlHwS+hyI UJVbTsKWhAAm1p0JQwWZa7sMXjmy0EQcv8V1KyMsoOFsWJP2Wfc8GiKdNJYL7L8R/ENOE4 f21QvfbExfcqSYuGXH8we8tQ85avShY= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-237-PC8YlrGYOumCFMPqCm78zA-1; Fri, 22 Oct 2021 15:05:22 -0400 X-MC-Unique: PC8YlrGYOumCFMPqCm78zA-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 56CA2801FCE; Fri, 22 Oct 2021 19:05:20 +0000 (UTC) Received: from warthog.procyon.org.uk (unknown [10.33.36.19]) by smtp.corp.redhat.com (Postfix) with ESMTP id 71C7E7092B; Fri, 22 Oct 2021 19:05:09 +0000 (UTC) Organization: Red Hat UK Ltd. 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Registered in England and Wales under Company Registration No. 3798903 Subject: [PATCH v2 26/53] vfs, fscache: Implement pinning of cache usage for writeback From: David Howells To: linux-cachefs@redhat.com Cc: dhowells@redhat.com, Trond Myklebust , Anna Schumaker , Steve French , Dominique Martinet , Jeff Layton , Matthew Wilcox , Alexander Viro , Omar Sandoval , Linus Torvalds , linux-afs@lists.infradead.org, linux-nfs@vger.kernel.org, linux-cifs@vger.kernel.org, ceph-devel@vger.kernel.org, v9fs-developer@lists.sourceforge.net, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Date: Fri, 22 Oct 2021 20:05:08 +0100 Message-ID: <163492950845.1038219.15215875412425428905.stgit@warthog.procyon.org.uk> In-Reply-To: <163492911924.1038219.13107463173777870713.stgit@warthog.procyon.org.uk> References: <163492911924.1038219.13107463173777870713.stgit@warthog.procyon.org.uk> User-Agent: StGit/0.23 MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 Precedence: bulk List-ID: X-Mailing-List: linux-cifs@vger.kernel.org Cachefiles has a problem in that it needs to keep the backing file for a cookie open whilst there are local modifications pending that need to be written to it. However, we don't want to keep the file open indefinitely, as that causes EMFILE/ENFILE/ENOMEM problems. Reopening the cache file, however, is a problem if this is being done due to writeback triggered by exit(). Some filesystems will oops if we try to open a file in that context because they want to access current->fs or other resources that have already been dismantled. To get around this, I added the following: (1) An inode flag, I_PINNING_FSCACHE_WB, to be set on a network filesystem inode to indicate that we have a usage count on the cookie caching that inode. (2) A flag in struct writeback_control, unpinned_fscache_wb, that is set when __writeback_single_inode() clears the last dirty page from i_pages - at which point it clears I_PINNING_FSCACHE_WB and sets this flag. This has to be done here so that clearing I_PINNING_FSCACHE_WB can be done atomically with the check of PAGECACHE_TAG_DIRTY that clears I_DIRTY_PAGES. (3) A function, fscache_set_page_dirty(), which if it is not set, sets I_PINNING_FSCACHE_WB and calls fscache_use_cookie() to pin the cache resources. (4) A function, fscache_unpin_writeback(), to be called by ->write_inode() to unuse the cookie. (5) A function, fscache_clear_inode_writeback(), to be called when the inode is evicted, before clear_inode() is called. This cleans up any lingering I_PINNING_FSCACHE_WB. The network filesystem can then use these tools to make sure that fscache_write_to_cache() can write locally modified data to the cache as well as to the server. For the future, I'm working on write helpers for netfs lib that should allow this facility to be removed by keeping track of the dirty regions separately - but that's incomplete at the moment and is also going to be affected by folios, one way or another, since it deals with pages Signed-off-by: David Howells cc: linux-cachefs@redhat.com --- fs/fs-writeback.c | 8 ++++++++ fs/fscache/io.c | 38 ++++++++++++++++++++++++++++++++++++++ include/linux/fs.h | 3 +++ include/linux/fscache.h | 40 ++++++++++++++++++++++++++++++++++++++++ include/linux/fscache_old.h | 1 + include/linux/writeback.h | 1 + 6 files changed, 91 insertions(+) diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c index 81ec192ce067..f3122831c4fe 100644 --- a/fs/fs-writeback.c +++ b/fs/fs-writeback.c @@ -1666,6 +1666,13 @@ __writeback_single_inode(struct inode *inode, struct writeback_control *wbc) if (mapping_tagged(mapping, PAGECACHE_TAG_DIRTY)) inode->i_state |= I_DIRTY_PAGES; + else if (unlikely(inode->i_state & I_PINNING_FSCACHE_WB)) { + if (!(inode->i_state & I_DIRTY_PAGES)) { + inode->i_state &= ~I_PINNING_FSCACHE_WB; + wbc->unpinned_fscache_wb = true; + dirty |= I_PINNING_FSCACHE_WB; /* Cause write_inode */ + } + } spin_unlock(&inode->i_lock); @@ -1675,6 +1682,7 @@ __writeback_single_inode(struct inode *inode, struct writeback_control *wbc) if (ret == 0) ret = err; } + wbc->unpinned_fscache_wb = false; trace_writeback_single_inode(inode, wbc, nr_to_write); return ret; } diff --git a/fs/fscache/io.c b/fs/fscache/io.c index 0c128e61df81..5b7ecb8a205b 100644 --- a/fs/fscache/io.c +++ b/fs/fscache/io.c @@ -217,6 +217,44 @@ int __fscache_fallback_write_page(struct fscache_cookie *cookie, struct page *pa } EXPORT_SYMBOL(__fscache_fallback_write_page); +/** + * fscache_set_page_dirty - Mark page dirty and pin a cache object for writeback + * @page: The page being dirtied + * @cookie: The cookie referring to the cache object + * + * Set the dirty flag on a page and pin an in-use cache object in memory when + * dirtying a page so that writeback can later write to it. This is intended + * to be called from the filesystem's ->set_page_dirty() method. + * + * Returns 1 if PG_dirty was set on the page, 0 otherwise. + */ +int fscache_set_page_dirty(struct page *page, struct fscache_cookie *cookie) +{ + struct inode *inode = page->mapping->host; + bool need_use = false; + + _enter(""); + + if (!__set_page_dirty_nobuffers(page)) + return 0; + if (!fscache_cookie_valid(cookie)) + return 1; + + if (!(inode->i_state & I_PINNING_FSCACHE_WB)) { + spin_lock(&inode->i_lock); + if (!(inode->i_state & I_PINNING_FSCACHE_WB)) { + inode->i_state |= I_PINNING_FSCACHE_WB; + need_use = true; + } + spin_unlock(&inode->i_lock); + + if (need_use) + fscache_use_cookie(cookie, true); + } + return 1; +} +EXPORT_SYMBOL(fscache_set_page_dirty); + struct fscache_write_request { struct netfs_cache_resources cache_resources; struct address_space *mapping; diff --git a/include/linux/fs.h b/include/linux/fs.h index e7a633353fd2..908ea452a2cf 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -2419,6 +2419,8 @@ static inline void kiocb_clone(struct kiocb *kiocb, struct kiocb *kiocb_src, * Used to detect that mark_inode_dirty() should not move * inode between dirty lists. * + * I_PINNING_FSCACHE_WB Inode is pinning an fscache object for writeback. + * * Q: What is the difference between I_WILL_FREE and I_FREEING? */ #define I_DIRTY_SYNC (1 << 0) @@ -2441,6 +2443,7 @@ static inline void kiocb_clone(struct kiocb *kiocb, struct kiocb *kiocb_src, #define I_CREATING (1 << 15) #define I_DONTCACHE (1 << 16) #define I_SYNC_QUEUED (1 << 17) +#define I_PINNING_FSCACHE_WB (1 << 18) #define I_DIRTY_INODE (I_DIRTY_SYNC | I_DIRTY_DATASYNC) #define I_DIRTY (I_DIRTY_INODE | I_DIRTY_PAGES) diff --git a/include/linux/fscache.h b/include/linux/fscache.h index 2996b417c5d0..46a89b5d7cfb 100644 --- a/include/linux/fscache.h +++ b/include/linux/fscache.h @@ -559,6 +559,46 @@ static inline void fscache_write_to_cache(struct fscache_cookie *cookie, } #endif /* FSCACHE_USE_NEW_IO_API */ +#if __fscache_available +extern int fscache_set_page_dirty(struct page *page, struct fscache_cookie *cookie); +#else +#define fscache_set_page_dirty(PAGE, COOKIE) (__set_page_dirty_nobuffers((PAGE))) +#endif + +/** + * fscache_unpin_writeback - Unpin writeback resources + * @wbc: The writeback control + * @cookie: The cookie referring to the cache object + * + * Unpin the writeback resources pinned by fscache_set_page_dirty(). This is + * intended to be called by the netfs's ->write_inode() method. + */ +static inline void fscache_unpin_writeback(struct writeback_control *wbc, + struct fscache_cookie *cookie) +{ + if (wbc->unpinned_fscache_wb) + fscache_unuse_cookie(cookie, NULL, NULL); +} + +/** + * fscache_clear_inode_writeback - Clear writeback resources pinned by an inode + * @cookie: The cookie referring to the cache object + * @inode: The inode to clean up + * @aux: Auxiliary data to apply to the inode + * + * Clear any writeback resources held by an inode when the inode is evicted. + * This must be called before clear_inode() is called. + */ +static inline void fscache_clear_inode_writeback(struct fscache_cookie *cookie, + struct inode *inode, + const void *aux) +{ + if (inode->i_state & I_PINNING_FSCACHE_WB) { + loff_t i_size = i_size_read(inode); + fscache_unuse_cookie(cookie, aux, &i_size); + } +} + #ifdef FSCACHE_USE_FALLBACK_IO_API /** diff --git a/include/linux/fscache_old.h b/include/linux/fscache_old.h index 01558d155799..ba4878b56717 100644 --- a/include/linux/fscache_old.h +++ b/include/linux/fscache_old.h @@ -19,6 +19,7 @@ #include #include #include +#include #include #if defined(CONFIG_FSCACHE) || defined(CONFIG_FSCACHE_MODULE) diff --git a/include/linux/writeback.h b/include/linux/writeback.h index d1f65adf6a26..2fda288600d3 100644 --- a/include/linux/writeback.h +++ b/include/linux/writeback.h @@ -69,6 +69,7 @@ struct writeback_control { unsigned for_reclaim:1; /* Invoked from the page allocator */ unsigned range_cyclic:1; /* range_start is cyclic */ unsigned for_sync:1; /* sync(2) WB_SYNC_ALL writeback */ + unsigned unpinned_fscache_wb:1; /* Cleared I_PINNING_FSCACHE_WB */ /* * When writeback IOs are bounced through async layers, only the