From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-18.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_GIT autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 7D6F5C433DB for ; Fri, 22 Jan 2021 16:08:43 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 51A752343E for ; Fri, 22 Jan 2021 16:08:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729467AbhAVQIG (ORCPT ); Fri, 22 Jan 2021 11:08:06 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44954 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729436AbhAVQHW (ORCPT ); Fri, 22 Jan 2021 11:07:22 -0500 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 54D03C061788; Fri, 22 Jan 2021 08:06:42 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=Content-Transfer-Encoding:MIME-Version: References:In-Reply-To:Message-Id:Date:Subject:Cc:To:From:Sender:Reply-To: Content-Type:Content-ID:Content-Description; bh=trvRejywQoT6u/VJzqGTxTieNBzKtlrLfHekLYCLg+E=; b=pkm7pd/SU24bpEMYVzjjiAch67 hGpQwHm3+s2B0OXEh/ZsWr5xDtyU/afV/WNdlSgV2T958XK//4rhmUZ+MmM24CV4Y2R/hpl7kj8wC 0BEzSdgRt90z1i3bGFNcPrD9ku5meM5JDg521s/Y0zmiBUNPcjo5rrL4SnviNsaSK0p0hUPA25fqp J4l5DhH+HwWRaqodqRako7iQPM83VuMzOaKkjEWBFJqGujoLBVQbURhpSPS9lzC+E+ztyKWJQYMun 0oeGs4T6XGgVb4zc1aGiFwy+dpvlddy8hM2f591kiM6PNty44uhrUd94LhPW5SE5+ULTdyOHZyZSe EAJl04nQ==; Received: from willy by casper.infradead.org with local (Exim 4.94 #2 (Red Hat Linux)) id 1l2yw9-000wM6-PT; Fri, 22 Jan 2021 16:05:37 +0000 From: "Matthew Wilcox (Oracle)" To: Andrew Morton Cc: "Matthew Wilcox (Oracle)" , linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Kent Overstreet , Christoph Hellwig Subject: [PATCH v5 06/18] mm/filemap: Support readpage splitting a page Date: Fri, 22 Jan 2021 16:01:28 +0000 Message-Id: <20210122160140.223228-7-willy@infradead.org> X-Mailer: git-send-email 2.29.2 In-Reply-To: <20210122160140.223228-1-willy@infradead.org> References: <20210122160140.223228-1-willy@infradead.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org For page splitting to succeed, the thread asking to split the page has to be the only one with a reference to the page. Calling wait_on_page_locked() while holding a reference to the page will effectively prevent this from happening with sufficient threads waiting on the same page. Use put_and_wait_on_page_locked() to sleep without holding a reference to the page, then retry the page lookup after the page is unlocked. Since we now get the page lock a little earlier in filemap_update_page(), we can eliminate a number of duplicate checks. The original intent (commit ebded02788b5 ("avoid unnecessary calls to lock_page when waiting for IO to complete during a read")) behind getting the page lock later was to avoid re-locking the page after it has been brought uptodate by another thread. We still avoid that because we go through the normal lookup path again after the winning thread has brought the page uptodate. Signed-off-by: Matthew Wilcox (Oracle) Reviewed-by: Kent Overstreet Reviewed-by: Christoph Hellwig --- mm/filemap.c | 76 ++++++++++++++++------------------------------------ 1 file changed, 23 insertions(+), 53 deletions(-) diff --git a/mm/filemap.c b/mm/filemap.c index c71cd95e5372b..88201506ad3ef 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -1368,14 +1368,6 @@ static int __wait_on_page_locked_async(struct page *page, return ret; } -static int wait_on_page_locked_async(struct page *page, - struct wait_page_queue *wait) -{ - if (!PageLocked(page)) - return 0; - return __wait_on_page_locked_async(compound_head(page), wait, false); -} - /** * put_and_wait_on_page_locked - Drop a reference and wait for it to be unlocked * @page: The page to wait for. @@ -2299,64 +2291,42 @@ static struct page *filemap_update_page(struct kiocb *iocb, struct file *filp, struct inode *inode = mapping->host; int error; - /* - * See comment in do_read_cache_page on why - * wait_on_page_locked is used to avoid unnecessarily - * serialisations and why it's safe. - */ if (iocb->ki_flags & IOCB_WAITQ) { - error = wait_on_page_locked_async(page, - iocb->ki_waitq); + error = lock_page_async(page, iocb->ki_waitq); + if (error) { + put_page(page); + return ERR_PTR(error); + } } else { - error = wait_on_page_locked_killable(page); - } - if (unlikely(error)) { - put_page(page); - return ERR_PTR(error); + if (!trylock_page(page)) { + put_and_wait_on_page_locked(page, TASK_KILLABLE); + return NULL; + } } - if (PageUptodate(page)) - return page; + if (!page->mapping) + goto truncated; + if (PageUptodate(page)) + goto uptodate; if (inode->i_blkbits == PAGE_SHIFT || !mapping->a_ops->is_partially_uptodate) - goto page_not_up_to_date; + goto readpage; /* pipes can't handle partially uptodate pages */ if (unlikely(iov_iter_is_pipe(iter))) - goto page_not_up_to_date; - if (!trylock_page(page)) - goto page_not_up_to_date; - /* Did it get truncated before we got the lock? */ - if (!page->mapping) - goto page_not_up_to_date_locked; + goto readpage; if (!mapping->a_ops->is_partially_uptodate(page, - pos & ~PAGE_MASK, count)) - goto page_not_up_to_date_locked; + pos & (thp_size(page) - 1), count)) + goto readpage; +uptodate: unlock_page(page); return page; -page_not_up_to_date: - /* Get exclusive access to the page ... */ - error = lock_page_for_iocb(iocb, page); - if (unlikely(error)) { - put_page(page); - return ERR_PTR(error); - } - -page_not_up_to_date_locked: - /* Did it get truncated before we got the lock? */ - if (!page->mapping) { - unlock_page(page); - put_page(page); - return NULL; - } - - /* Did somebody else fill it already? */ - if (PageUptodate(page)) { - unlock_page(page); - return page; - } - +readpage: return filemap_read_page(iocb, filp, mapping, page); +truncated: + unlock_page(page); + put_page(page); + return NULL; } static struct page *filemap_create_page(struct kiocb *iocb, -- 2.29.2