From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out30-101.freemail.mail.aliyun.com (out30-101.freemail.mail.aliyun.com [115.124.30.101]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 628373595E for ; Mon, 6 Jan 2025 06:29:54 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=115.124.30.101 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1736144997; cv=none; b=cdKlXhP/44zBvNTgwQgWebO7txhQ6FQcGqS/aC1SxbOI5o/gPLY4hG6RSjHR/1XaSciaFnWA6jsbRxwsHkQuAdXm35wRk2gcmMkMQCZCY1ZrnSkH/jmZkSzmYkdEkOebhciCu+sbCUgvZ3zvz/G8HcK+earwXjJCr9hR6o6VHvM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1736144997; c=relaxed/simple; bh=cCcgeClPGFCuLW7f5SWNK8HC8OnGZi2ROGTQniwwJgs=; h=Message-ID:Date:MIME-Version:Subject:From:To:Cc:References: In-Reply-To:Content-Type; b=EybBYy7EbxjxsHG0+cgekpQOWDfT1tB5UKPDvAWYKKGLYPSC1wk/7WFnjt7//UJbx+cRAxTfjgOCiAPArx96YtymUJWzMvbkqfMOg/L7wceAruxIgFGChBw3pMVz9xpQ8E2y4qTKvF0DFBedj4GSWlkshEd9+W7lCpNLU6XwzF4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com; spf=pass smtp.mailfrom=linux.alibaba.com; dkim=pass (1024-bit key) header.d=linux.alibaba.com header.i=@linux.alibaba.com header.b=PMp+mwd7; arc=none smtp.client-ip=115.124.30.101 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.alibaba.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.alibaba.com header.i=@linux.alibaba.com header.b="PMp+mwd7" DKIM-Signature:v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.alibaba.com; s=default; t=1736144987; h=Message-ID:Date:MIME-Version:Subject:From:To:Content-Type; bh=2rp5d/NXdTPCy798TF4avcBe63oyb+Kp3kLESZ7ZCUk=; b=PMp+mwd7L3QMaLd+pXHPLygrF8K6KCf+DH+JE2T6oXZvsNGo84dISVGtmZ+Vk2Br8Yc9dbxQPN7esKz6tuOVSiW6cagM0QQ/vjUZmnh+D00J708pjsQQUkjRCAdUVHL/4yydsrrvgE3dO1TCD2fGLADVNVUbJtPjERHFvFSQCVU= Received: from 30.74.144.118(mailfrom:baolin.wang@linux.alibaba.com fp:SMTPD_---0WN.XSw9_1736144985 cluster:ay36) by smtp.aliyun-inc.com; Mon, 06 Jan 2025 14:29:46 +0800 Message-ID: Date: Mon, 6 Jan 2025 14:29:45 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2] mm: shmem: skip swapcache for swapin of synchronous swap device From: Baolin Wang To: Matthew Wilcox Cc: akpm@linux-foundation.org, hughd@google.com, david@redhat.com, wangkefeng.wang@huawei.com, kasong@tencent.com, ying.huang@linux.alibaba.com, 21cnbao@gmail.com, ryan.roberts@arm.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <04997e54c276eff40a6119a90d36a4e71aade89c.1735806921.git.baolin.wang@linux.alibaba.com> <8344980d-4c22-4694-9a76-2e5a7ada50cb@linux.alibaba.com> In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 2025/1/6 12:59, Baolin Wang wrote: > > > On 2025/1/6 12:07, Matthew Wilcox wrote: >> On Mon, Jan 06, 2025 at 11:46:04AM +0800, Baolin Wang wrote: >>> On 2025/1/2 21:10, Matthew Wilcox wrote: >>>> On Thu, Jan 02, 2025 at 04:40:17PM +0800, Baolin Wang wrote: >>>>> With fast swap devices (such as zram), swapin latency is crucial to >>>>> applications. >>>>> For shmem swapin, similar to anonymous memory swapin, we can skip >>>>> the swapcache >>>>> operation to improve swapin latency. >>>> >>>> OK, but now we have more complexity.  Why can't we always skip the >>>> swapcache on swapin? >>> >>> Skipping swapcache is used to swap-in shmem large folios, avoiding >>> the large >>> folios being split. Meanwhile, since the IO latency of syncing swap >>> devices >>> is relatively small, it won't cause the IO latency amplification issue. >>> >>> But for async swap devices, if we swap-in the large folio one-time, I am >>> afraid the IO latency can be amplified. And I remember we still haven't >>> reached an agreement here[1], so let's step by step and start with >>> the sync >>> swap devices first. >> >> Regardless of whether we choose to swap-in an order-0 or a large folio, >> my point is that we should always do it to the pagecache rather than the >> swap cache. > > IMO, this would miss the swap readahead algorithm in the swap case, > which can benefit the order-0 swap-in. We need more work to ensure that > skipping swapcache is helpful for all cases, which is why I'm starting > with sync swap devices first. BTW, I used the SSD swap device to test the performance of skipping swapcache with the following hack changes, and I found that the performance of order-0 sequential swap-in shows a significant regression. Without the following changes: 1G order-0 shmem swap-in: 8056 ms With the following changes (skip swapcache): 1G order-0 shmem swap-in: 38536 ms diff --git a/mm/page_io.c b/mm/page_io.c index 9b983de351f9..1e22dedcd584 100644 --- a/mm/page_io.c +++ b/mm/page_io.c @@ -620,7 +620,6 @@ void swap_read_folio(struct folio *folio, struct swap_iocb **plug) unsigned long pflags; bool in_thrashing; - VM_BUG_ON_FOLIO(!folio_test_swapcache(folio) && !synchronous, folio); VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio); VM_BUG_ON_FOLIO(folio_test_uptodate(folio), folio); diff --git a/mm/shmem.c b/mm/shmem.c index e82ef1ef1c68..2902d3477520 100644 --- a/mm/shmem.c +++ b/mm/shmem.c @@ -2295,7 +2295,7 @@ static int shmem_swapin_folio(struct inode *inode, pgoff_t index, fallback_order0 = true; /* Skip swapcache for synchronous device. */ - if (!fallback_order0 && data_race(si->flags & SWP_SYNCHRONOUS_IO)) { + if (!fallback_order0) { folio = shmem_swap_alloc_folio(inode, vma, index, swap, order, gfp); if (!IS_ERR(folio)) { skip_swapcache = true;