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=-0.6 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no 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 B374DC433E0 for ; Fri, 19 Jun 2020 11:56:08 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8BFAE2083B for ; Fri, 19 Jun 2020 11:56:08 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="YmQH+Tq3" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732803AbgFSL4D (ORCPT ); Fri, 19 Jun 2020 07:56:03 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55424 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1732225AbgFSL4B (ORCPT ); Fri, 19 Jun 2020 07:56:01 -0400 Received: from bombadil.infradead.org (bombadil.infradead.org [IPv6:2607:7c80:54:e::133]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 97E19C06174E; Fri, 19 Jun 2020 04:56:01 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20170209; h=In-Reply-To:Content-Type:MIME-Version :References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=qkiSuMBHq1jJPg79H69BLQzOTNgh3NSXy1sjSUD7sso=; b=YmQH+Tq34JCOA4Fpp+Ct6KEZnt 8L0h3XQhFTfcl+EZx9PD/QmFfjIZnpy4HoPgNnfBqHv64Iq5KfuRrtvHpLcfBtAlvvzZLZIa6wd8f WBdUMayWL2szYgJzuQAOr0qIZuM5ocftxFPIzNGVjJSWVMSlvpoZeOYI4S4AGQO8Nb0yis8YPFDTs gFrJkRAnXtTDuea5wOUzzuns5noEUpSfRbZfvMS0JhmrqudLco3NaWgMJzebBPpoOvVOvwgRaFW3F NclEHximP3q4U57rebPA25c4PcGKBj5TM+IBkvwcGuWphYM+ITP6Po2I7wixaC/wuvOd6BghDK1It 5dgYN/wg==; Received: from willy by bombadil.infradead.org with local (Exim 4.92.3 #3 (Red Hat Linux)) id 1jmFcc-0002c8-O0; Fri, 19 Jun 2020 11:55:50 +0000 Date: Fri, 19 Jun 2020 04:55:50 -0700 From: Matthew Wilcox To: Andreas Gruenbacher Cc: Linus Torvalds , Andrew Morton , linux-xfs , Junxiao Bi , William Kucharski , Joseph Qi , John Hubbard , linux-kernel@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net, cluster-devel@redhat.com, linux-mm@kvack.org, ocfs2-devel@oss.oracle.com, linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org, linux-erofs@lists.ozlabs.org, Christoph Hellwig , linux-btrfs@vger.kernel.org Subject: Re: [PATCH 2/2] gfs2: Rework read and page fault locking Message-ID: <20200619115550.GY8681@bombadil.infradead.org> References: <20200619093916.1081129-1-agruenba@redhat.com> <20200619093916.1081129-3-agruenba@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200619093916.1081129-3-agruenba@redhat.com> Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Fri, Jun 19, 2020 at 11:39:16AM +0200, Andreas Gruenbacher wrote: > static int gfs2_readpage(struct file *file, struct page *page) > { > - struct address_space *mapping = page->mapping; > - struct gfs2_inode *ip = GFS2_I(mapping->host); > - struct gfs2_holder gh; > int error; > > - unlock_page(page); > - gfs2_holder_init(ip->i_gl, LM_ST_SHARED, 0, &gh); > - error = gfs2_glock_nq(&gh); > - if (unlikely(error)) > - goto out; > - error = AOP_TRUNCATED_PAGE; > - lock_page(page); > - if (page->mapping == mapping && !PageUptodate(page)) > - error = __gfs2_readpage(file, page); > - else > - unlock_page(page); > - gfs2_glock_dq(&gh); > -out: > - gfs2_holder_uninit(&gh); > - if (error && error != AOP_TRUNCATED_PAGE) > + error = __gfs2_readpage(file, page); > + if (error) > lock_page(page); > return error; I don't think this is right. If you return an error from ->readpage, I'm pretty sure you're supposed to unlock that page. Looking at generic_file_buffered_read(): error = mapping->a_ops->readpage(filp, page); if (unlikely(error)) { if (error == AOP_TRUNCATED_PAGE) { put_page(page); error = 0; goto find_page; } goto readpage_error; } ... readpage_error: put_page(page); goto out; ... out: ra->prev_pos = prev_index; ra->prev_pos <<= PAGE_SHIFT; ra->prev_pos |= prev_offset; *ppos = ((loff_t)index << PAGE_SHIFT) + offset; file_accessed(filp); return written ? written : error; so we don't call unlock_page() in generic code, which means the next time we try to get this page, we'll do ... page = find_get_page(mapping, index); ... if (!PageUptodate(page)) { error = wait_on_page_locked_killable(page); and presumably we'll wait forever because nobody is going to unlock this page? > @@ -598,16 +582,9 @@ static void gfs2_readahead(struct readahead_control *rac) > { > struct inode *inode = rac->mapping->host; > struct gfs2_inode *ip = GFS2_I(inode); > - struct gfs2_holder gh; > > - gfs2_holder_init(ip->i_gl, LM_ST_SHARED, 0, &gh); > - if (gfs2_glock_nq(&gh)) > - goto out_uninit; > if (!gfs2_is_stuffed(ip)) > mpage_readahead(rac, gfs2_block_map); > - gfs2_glock_dq(&gh); > -out_uninit: > - gfs2_holder_uninit(&gh); > } Not for this patch, obviously, but why do you go to the effort of using iomap_readpage() to implement gfs2_readpage(), but don't use iomap for gfs2_readahead()? Far more pages are brought in through ->readahead than are brought in through ->readpage. > static ssize_t gfs2_file_read_iter(struct kiocb *iocb, struct iov_iter *to) > { > + struct gfs2_inode *ip; > + struct gfs2_holder gh; > + size_t written = 0; > ssize_t ret; > > + gfs2_holder_mark_uninitialized(&gh); > if (iocb->ki_flags & IOCB_DIRECT) { > ret = gfs2_file_direct_read(iocb, to); Again, future work, but you probably want to pass in &gh here so you don't have to eat up another 32 bytes or so of stack space on an unused gfs2_holder. > if (likely(ret != -ENOTBLK)) > return ret; > iocb->ki_flags &= ~IOCB_DIRECT; > } > - return generic_file_read_iter(iocb, to); > + iocb->ki_flags |= IOCB_CACHED; > + ret = generic_file_read_iter(iocb, to); > + iocb->ki_flags &= ~IOCB_CACHED; > + if (ret >= 0) { > + if (!iov_iter_count(to)) > + return ret; > + written = ret; > + } else { > + switch(ret) { > + case -EAGAIN: > + if (iocb->ki_flags & IOCB_NOWAIT) > + return ret; > + break; > + case -ECANCELED: > + break; > + default: > + return ret; > + } > + } I'm wondering if we want to do this in common code rather than making it something special only a few filesystems do (either because they care about workloads with many threads accessing the same file, or because their per-file locks are very heavy-weight).