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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 9E9C4C433FE for ; Fri, 25 Mar 2022 01:13:45 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1353486AbiCYBPP (ORCPT ); Thu, 24 Mar 2022 21:15:15 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:45164 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1355509AbiCYBPM (ORCPT ); Thu, 24 Mar 2022 21:15:12 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 740AB62D0 for ; Thu, 24 Mar 2022 18:13:37 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id 1C7A7B82707 for ; Fri, 25 Mar 2022 01:13:36 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id A4E3CC340F1; Fri, 25 Mar 2022 01:13:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1648170814; bh=3E0/tCjb2pNNNXDeU0Do5PPCZGnwid1h5jhGzuv2tdg=; h=Date:To:From:In-Reply-To:Subject:From; b=hie0A/Zef92KCm1Nfx7CiAs3Ff9dT2vSwdXg9hOH1IBzyMLa5+aTSgHOXu1Yjbhwa 1Kx2Ib11n6bwenVKgRiSJelNdJEis+2XOibXzxy7js38AsIGsObLi43Og7siZr9s4Q vnMaIDFwQH0rUfQh6bxOB5h6hWL4cv8KvP59I0VQ= Date: Thu, 24 Mar 2022 18:13:34 -0700 To: zhangliang5@huawei.com, willy@infradead.org, vbabka@suse.cz, shy828301@gmail.com, shakeelb@google.com, rppt@linux.ibm.com, roman.gushchin@linux.dev, rientjes@google.com, riel@surriel.com, peterx@redhat.com, oleg@redhat.com, nadav.amit@gmail.com, mike.kravetz@oracle.com, mhocko@kernel.org, kirill.shutemov@linux.intel.com, jhubbard@nvidia.com, jgg@nvidia.com, jannh@google.com, jack@suse.cz, hughd@google.com, hch@lst.de, ddutile@redhat.com, aarcange@redhat.com, david@redhat.com, akpm@linux-foundation.org, patches@lists.linux.dev, linux-mm@kvack.org, mm-commits@vger.kernel.org, torvalds@linux-foundation.org, akpm@linux-foundation.org From: Andrew Morton In-Reply-To: <20220324180758.96b1ac7e17675d6bc474485e@linux-foundation.org> Subject: [patch 100/114] mm: optimize do_wp_page() for fresh pages in local LRU pagevecs Message-Id: <20220325011334.A4E3CC340F1@smtp.kernel.org> Precedence: bulk Reply-To: linux-kernel@vger.kernel.org List-ID: X-Mailing-List: mm-commits@vger.kernel.org From: David Hildenbrand Subject: mm: optimize do_wp_page() for fresh pages in local LRU pagevecs For example, if a page just got swapped in via a read fault, the LRU pagevecs might still hold a reference to the page. If we trigger a write fault on such a page, the additional reference from the LRU pagevecs will prohibit reusing the page. Let's conditionally drain the local LRU pagevecs when we stumble over a !PageLRU() page. We cannot easily drain remote LRU pagevecs and it might not be desirable performance-wise. Consequently, this will only avoid copying in some cases. Add a simple "page_count(page) > 3" check first but keep the "page_count(page) > 1 + PageSwapCache(page)" check in place, as we want to minimize cases where we remove a page from the swapcache but won't be able to reuse it, for example, because another process has it mapped R/O, to not affect reclaim. We cannot easily handle the following cases and we will always have to copy: (1) The page is referenced in the LRU pagevecs of other CPUs. We really would have to drain the LRU pagevecs of all CPUs -- most probably copying is much cheaper. (2) The page is already PageLRU() but is getting moved between LRU lists, for example, for activation (e.g., mark_page_accessed()), deactivation (MADV_COLD), or lazyfree (MADV_FREE). We'd have to drain mostly unconditionally, which might be bad performance-wise. Most probably this won't happen too often in practice. Note that there are other reasons why an anon page might temporarily not be PageLRU(): for example, compaction and migration have to isolate LRU pages from the LRU lists first (isolate_lru_page()), moving them to temporary local lists and clearing PageLRU() and holding an additional reference on the page. In that case, we'll always copy. This change seems to be fairly effective with the reproducer [1] shared by Nadav, as long as writeback is done synchronously, for example, using zram. However, with asynchronous writeback, we'll usually fail to free the swapcache because the page is still under writeback: something we cannot easily optimize for, and maybe it's not really relevant in practice. [1] https://lkml.kernel.org/r/0480D692-D9B2-429A-9A88-9BBA1331AC3A@gmail.com Link: https://lkml.kernel.org/r/20220131162940.210846-3-david@redhat.com Signed-off-by: David Hildenbrand Acked-by: Vlastimil Babka Cc: Andrea Arcangeli Cc: Christoph Hellwig Cc: David Rientjes Cc: Don Dutile Cc: Hugh Dickins Cc: Jan Kara Cc: Jann Horn Cc: Jason Gunthorpe Cc: John Hubbard Cc: Kirill A. Shutemov Cc: Liang Zhang Cc: Matthew Wilcox (Oracle) Cc: Michal Hocko Cc: Mike Kravetz Cc: Mike Rapoport Cc: Nadav Amit Cc: Oleg Nesterov Cc: Peter Xu Cc: Rik van Riel Cc: Roman Gushchin Cc: Shakeel Butt Cc: Yang Shi Signed-off-by: Andrew Morton --- mm/memory.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-) --- a/mm/memory.c~mm-optimize-do_wp_page-for-fresh-pages-in-local-lru-pagevecs +++ a/mm/memory.c @@ -3294,7 +3294,15 @@ static vm_fault_t do_wp_page(struct vm_f * * PageKsm() doesn't necessarily raise the page refcount. */ - if (PageKsm(page) || page_count(page) > 1 + PageSwapCache(page)) + if (PageKsm(page) || page_count(page) > 3) + goto copy; + if (!PageLRU(page)) + /* + * Note: We cannot easily detect+handle references from + * remote LRU pagevecs or references to PageLRU() pages. + */ + lru_add_drain(); + if (page_count(page) > 1 + PageSwapCache(page)) goto copy; if (!trylock_page(page)) goto copy; _