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=-8.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED 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 6E40EC432BE for ; Fri, 30 Jul 2021 17:28:56 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id E3F9260F5C for ; Fri, 30 Jul 2021 17:28:55 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org E3F9260F5C Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=xmission.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=kvack.org Received: by kanga.kvack.org (Postfix) id 280B26B0033; Fri, 30 Jul 2021 13:28:55 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 231BB8D0001; Fri, 30 Jul 2021 13:28:55 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 11FDD6B005D; Fri, 30 Jul 2021 13:28:55 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0021.hostedemail.com [216.40.44.21]) by kanga.kvack.org (Postfix) with ESMTP id EA2CA6B0033 for ; Fri, 30 Jul 2021 13:28:54 -0400 (EDT) Received: from smtpin30.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay05.hostedemail.com (Postfix) with ESMTP id 8CA0D18030427 for ; Fri, 30 Jul 2021 17:28:54 +0000 (UTC) X-FDA: 78419939388.30.0F8A82B Received: from out02.mta.xmission.com (out02.mta.xmission.com [166.70.13.232]) by imf14.hostedemail.com (Postfix) with ESMTP id 243DE600BF34 for ; Fri, 30 Jul 2021 17:28:53 +0000 (UTC) Received: from in02.mta.xmission.com ([166.70.13.52]:45382) by out02.mta.xmission.com with esmtps (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.93) (envelope-from ) id 1m9WJT-00C0vz-8O; Fri, 30 Jul 2021 11:28:47 -0600 Received: from ip68-227-160-95.om.om.cox.net ([68.227.160.95]:50210 helo=email.xmission.com) by in02.mta.xmission.com with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.93) (envelope-from ) id 1m9WJR-00EIHz-PZ; Fri, 30 Jul 2021 11:28:46 -0600 From: ebiederm@xmission.com (Eric W. Biederman) To: Tiberiu A Georgescu Cc: akpm@linux-foundation.org, viro@zeniv.linux.org.uk, peterx@redhat.com, david@redhat.com, christian.brauner@ubuntu.com, adobriyan@gmail.com, songmuchun@bytedance.com, axboe@kernel.dk, vincenzo.frascino@arm.com, catalin.marinas@arm.com, peterz@infradead.org, chinwen.chang@mediatek.com, linmiaohe@huawei.com, jannh@google.com, apopple@nvidia.com, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, ivan.teterevkov@nutanix.com, florian.schmidt@nutanix.com, carl.waldspurger@nutanix.com, jonathan.davies@nutanix.com References: <20210730160826.63785-1-tiberiu.georgescu@nutanix.com> Date: Fri, 30 Jul 2021 12:28:17 -0500 In-Reply-To: <20210730160826.63785-1-tiberiu.georgescu@nutanix.com> (Tiberiu A. Georgescu's message of "Fri, 30 Jul 2021 16:08:25 +0000") Message-ID: <87y29nbtji.fsf@disp2133> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-XM-SPF: eid=1m9WJR-00EIHz-PZ;;;mid=<87y29nbtji.fsf@disp2133>;;;hst=in02.mta.xmission.com;;;ip=68.227.160.95;;;frm=ebiederm@xmission.com;;;spf=neutral X-XM-AID: U2FsdGVkX1+6IEKtMRYJExMJRTDSbxhxN5Cr2lmSlHE= X-SA-Exim-Connect-IP: 68.227.160.95 X-SA-Exim-Mail-From: ebiederm@xmission.com Subject: Re: [PATCH 0/1] pagemap: swap location for shared pages X-SA-Exim-Version: 4.2.1 (built Sat, 08 Feb 2020 21:53:50 +0000) X-SA-Exim-Scanned: Yes (on in02.mta.xmission.com) X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 243DE600BF34 Authentication-Results: imf14.hostedemail.com; dkim=none; spf=pass (imf14.hostedemail.com: domain of ebiederm@xmission.com designates 166.70.13.232 as permitted sender) smtp.mailfrom=ebiederm@xmission.com; dmarc=pass (policy=none) header.from=xmission.com X-Stat-Signature: 77bf6ddnujjng88ahz4xk841sgsnzzeb X-HE-Tag: 1627666133-904238 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: Tiberiu A Georgescu writes: > This patch follows up on a previous RFC: > 20210714152426.216217-1-tiberiu.georgescu@nutanix.com > > When a page allocated using the MAP_SHARED flag is swapped out, its pagemap > entry is cleared. In many cases, there is no difference between swapped-out > shared pages and newly allocated, non-dirty pages in the pagemap > interface. What is the point? You say a shared swapped out page is the same as a clean shared page and you are exactly correct. What is the point in knowing a shared page was swapped out? What does is the gain? I tried to understand the point by looking at your numbers below and everything I could see looked worse post patch. Eric > Example pagemap-test code (Tested on Kernel Version 5.14-rc3): > #define NPAGES (256) > /* map 1MiB shared memory */ > size_t pagesize = getpagesize(); > char *p = mmap(NULL, pagesize * NPAGES, PROT_READ | PROT_WRITE, > MAP_ANONYMOUS | MAP_SHARED, -1, 0); > /* Dirty new pages. */ > for (i = 0; i < PAGES; i++) > p[i * pagesize] = i; > > Run the above program in a small cgroup, which causes swapping: > /* Initialise cgroup & run a program */ > $ echo 512K > foo/memory.limit_in_bytes > $ echo 60 > foo/memory.swappiness > $ cgexec -g memory:foo ./pagemap-test > > Check the pagemap report. Example of the current expected output: > $ dd if=/proc/$PID/pagemap ibs=8 skip=$(($VADDR / $PAGESIZE)) count=$COUNT | hexdump -C > 00000000 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................| > * > 00000710 e1 6b 06 00 00 00 00 a1 9e eb 06 00 00 00 00 a1 |.k..............| > 00000720 6b ee 06 00 00 00 00 a1 a5 a4 05 00 00 00 00 a1 |k...............| > 00000730 5c bf 06 00 00 00 00 a1 90 b6 06 00 00 00 00 a1 |\...............| > > The first pagemap entries are reported as zeroes, indicating the pages have > never been allocated while they have actually been swapped out. > > This patch addresses the behaviour and modifies pte_to_pagemap_entry() to > make use of the XArray associated with the virtual memory area struct > passed as an argument. The XArray contains the location of virtual pages in > the page cache, swap cache or on disk. If they are in either of the caches, > then the original implementation still works. If not, then the missing > information will be retrieved from the XArray. > > Performance > ============ > I measured the performance of the patch on a single socket Xeon E5-2620 > machine, with 128GiB of RAM and 128GiB of swap storage. These were the > steps taken: > > 1. Run example pagemap-test code on a cgroup > a. Set up cgroup with limit_in_bytes=4GiB and swappiness=60; > b. allocate 16GiB (about 4 million pages); > c. dirty 0,50 or 100% of pages; > d. do this for both private and shared memory. > 2. Run `dd if= ibs=8 skip=$(($VADDR / $PAGESIZE)) count=4194304` > for each possible configuration above > a. 3 times for warm up; > b. 10 times to measure performance. > Use `time` or another performance measuring tool. > > Results (averaged over 10 iterations): > +--------+------------+------------+ > | dirty% | pre patch | post patch | > +--------+------------+------------+ > private|anon | 0% | 8.15s | 8.40s | > | 50% | 11.83s | 12.19s | > | 100% | 12.37s | 12.20s | > +--------+------------+------------+ > shared|anon | 0% | 8.17s | 8.18s | > | 50% | (*) 10.43s | 37.43s | > | 100% | (*) 10.20s | 38.59s | > +--------+------------+------------+ > > (*): reminder that pre-patch produces incorrect pagemap entries for swapped > out pages. > > From run to run the above results are stable (mostly <1% stderr). > > The amount of time it takes for a full read of the pagemap depends on the > granularity used by dd to read the pagemap file. Even though the access is > sequential, the script only reads 8 bytes at a time, running pagemap_read() > COUNT times (one time for each page in a 16GiB area). > > To reduce overhead, we can use batching for large amounts of sequential > access. We can make dd read multiple page entries at a time, > allowing the kernel to make optimisations and yield more throughput. > > Performance in real time (seconds) of > `dd if= ibs=8*$BATCH skip=$(($VADDR / $PAGESIZE / $BATCH)) > count=$((4194304 / $BATCH))`: > +---------------------------------+ +---------------------------------+ > | Shared, Anon, 50% dirty | | Shared, Anon, 100% dirty | > +-------+------------+------------+ +-------+------------+------------+ > | Batch | Pre-patch | Post-patch | | Batch | Pre-patch | Post-patch | > +-------+------------+------------+ +-------+------------+------------+ > | 1 | (*) 10.43s | 37.43s | | 1 | (*) 10.20s | 38.59s | > | 2 | (*) 5.25s | 18.77s | | 2 | (*) 5.15s | 19.37s | > | 4 | (*) 2.63s | 9.42s | | 4 | (*) 2.63s | 9.74s | > | 8 | (*) 1.38s | 4.80s | | 8 | (*) 1.35s | 4.94s | > | 16 | (*) 0.73s | 2.46s | | 16 | (*) 0.72s | 2.54s | > | 32 | (*) 0.40s | 1.31s | | 32 | (*) 0.41s | 1.34s | > | 64 | (*) 0.25s | 0.72s | | 64 | (*) 0.24s | 0.74s | > | 128 | (*) 0.16s | 0.43s | | 128 | (*) 0.16s | 0.44s | > | 256 | (*) 0.12s | 0.28s | | 256 | (*) 0.12s | 0.29s | > | 512 | (*) 0.10s | 0.21s | | 512 | (*) 0.10s | 0.22s | > | 1024 | (*) 0.10s | 0.20s | | 1024 | (*) 0.10s | 0.21s | > +-------+------------+------------+ +-------+------------+------------+ > > To conclude, in order to make the most of the underlying mechanisms of > pagemap and xarray, one should be using batching to achieve better > performance. > > Future Work > ============ > > Note: there are PTE flags which currently do not survive the swap out when > the page is shmem: SOFT_DIRTY and UFFD_WP. > > A solution for saving the state of the UFFD_WP flag has been proposed by > Peter Xu in the patch linked below. The concept and mechanism proposed > could be extended to include the SOFT_DIRTY bit as well: > 20210715201422.211004-1-peterx@redhat.com > Our patches are mostly orthogonal. > > Kind regards, > Tibi > > Tiberiu A Georgescu (1): > pagemap: report swap location for shared pages > > fs/proc/task_mmu.c | 38 ++++++++++++++++++++++++++++++-------- > 1 file changed, 30 insertions(+), 8 deletions(-)