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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 1DE4BC433EF for ; Tue, 1 Feb 2022 21:31:29 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 459238D008F; Tue, 1 Feb 2022 16:31:29 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 3E28B8D0077; Tue, 1 Feb 2022 16:31:29 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 25BD08D008F; Tue, 1 Feb 2022 16:31:29 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0227.hostedemail.com [216.40.44.227]) by kanga.kvack.org (Postfix) with ESMTP id 157E98D0077 for ; Tue, 1 Feb 2022 16:31:29 -0500 (EST) Received: from smtpin20.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay03.hostedemail.com (Postfix) with ESMTP id B0D1085F19BE for ; Tue, 1 Feb 2022 21:31:28 +0000 (UTC) X-FDA: 79095507456.20.E244CC8 Received: from mail-ed1-f47.google.com (mail-ed1-f47.google.com [209.85.208.47]) by imf19.hostedemail.com (Postfix) with ESMTP id 6432A1A0004 for ; Tue, 1 Feb 2022 21:31:28 +0000 (UTC) Received: by mail-ed1-f47.google.com with SMTP id u18so36912820edt.6 for ; Tue, 01 Feb 2022 13:31:28 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=S9lNa69aK/8vUL9n02wvSyCGjVDmqQna9TX/zBr/ys0=; b=QrhqksDyHOFRKPb0vfkDGlm+V5uj4BnwW/A7kb1iVUX/M37YdFaGQ2X6pK9W/v1o+a Q/jcsrfL9MvI18gSRnUraSNq2NoKdMdcP2sW/yvHe1FupDH5l3p2908nvKja3iO16Z2B B8d4bimRbcq9Y+9uJboDNiF2vFKJwHTE3v5Kc6WIP3sKUMSfk4JITDWvrmsY6QCrzquo pjc4lBxuTFDZKwdH8TdpK9y362hy6H05dOh6y3kYPigmtbXnRUBkaVxOk686AxMtiTL1 AQiV7INkC7e6VFb2EvBU/M/A7gVLA3IqvGactZTe7jUUBc9tNXWRiUzJGJb9lAdlG1Hd ABfA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=S9lNa69aK/8vUL9n02wvSyCGjVDmqQna9TX/zBr/ys0=; b=yvKZNTMLFFkjTLYSIzxxpuDaxZeOp9HNHW4GBnA09z0YMVvCXuFuq6ln3BZZJwC5EJ zyWBd6Alj83cKl21CHYB5JwkUaNiCoK0g4Pn2IPOqF2iSLd5t9vc/zNiVj3+r9eOz7rC G6HE9gBINC1ARfmRaMbGd4XtBL80UYcvEpJWCP+2ZHoQrKsPZhF1J8N/4Ho6GZkCTh+W Es1fz4FJiAlLOc+jyDwg1NW4ifkEbmt4V8zdZxe0TqLwM6w+oImWi+pfPEnzYuI+0ZVS lHzzSyJJTHmbqxygMyaLe9bZMfqOhKM0LJIPJlisA/kghpH8nPUD+wejV+VeB1TEZIE6 ApLQ== X-Gm-Message-State: AOAM533GVYX91JVeWGZiLsbxOYPH20r7pI3e/f7OqSfjj0TsdLEOIwDZ vo4L3NO0alpz6QqX+B7XKV4omeJyEsfeWOrS/M4= X-Google-Smtp-Source: ABdhPJyP99qXgzmwdrP/3OeAwaj6wWvdxYGmpx/oAUSkJlbw+u9nwLPNf1AlnL0aoF6iq0hV9BTUApeqcqK/Xgpbl1U= X-Received: by 2002:a50:fd91:: with SMTP id o17mr27530607edt.127.1643751086964; Tue, 01 Feb 2022 13:31:26 -0800 (PST) MIME-Version: 1.0 References: <20220131162940.210846-1-david@redhat.com> <20220131162940.210846-7-david@redhat.com> In-Reply-To: <20220131162940.210846-7-david@redhat.com> From: Yang Shi Date: Tue, 1 Feb 2022 13:31:14 -0800 Message-ID: Subject: Re: [PATCH v3 6/9] mm/khugepaged: remove reuse_swap_page() usage To: David Hildenbrand Cc: Linux Kernel Mailing List , Andrew Morton , Hugh Dickins , Linus Torvalds , David Rientjes , Shakeel Butt , John Hubbard , Jason Gunthorpe , Mike Kravetz , Mike Rapoport , "Kirill A . Shutemov" , Matthew Wilcox , Vlastimil Babka , Jann Horn , Michal Hocko , Nadav Amit , Rik van Riel , Roman Gushchin , Andrea Arcangeli , Peter Xu , Donald Dutile , Christoph Hellwig , Oleg Nesterov , Jan Kara , Liang Zhang , Linux MM Content-Type: text/plain; charset="UTF-8" X-Rspam-User: nil X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 6432A1A0004 X-Stat-Signature: xrpe837c4dq5tnuyff1t48uqte1a9pt6 Authentication-Results: imf19.hostedemail.com; dkim=pass header.d=gmail.com header.s=20210112 header.b=QrhqksDy; spf=pass (imf19.hostedemail.com: domain of shy828301@gmail.com designates 209.85.208.47 as permitted sender) smtp.mailfrom=shy828301@gmail.com; dmarc=pass (policy=none) header.from=gmail.com X-HE-Tag: 1643751088-439279 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: On Mon, Jan 31, 2022 at 8:33 AM David Hildenbrand wrote: > > reuse_swap_page() currently indicates if we can write to an anon page > without COW. A COW is required if the page is shared by multiple > processes (either already mapped or via swap entries) or if there is > concurrent writeback that cannot tolerate concurrent page modifications. > > However, in the context of khugepaged we're not actually going to write > to a read-only mapped page, we'll copy the page content to our newly > allocated THP and map that THP writable. All we have to make sure > is that the read-only mapped page we're about to copy won't get reused > by another process sharing the page, otherwise, page content would > get modified. But that is already guaranteed via multiple mechanisms > (e.g., holding a reference, holding the page lock, removing the rmap after > copying the page). > > The swapcache handling was introduced in commit 10359213d05a ("mm: > incorporate read-only pages into transparent huge pages") and it sounds > like it merely wanted to mimic what do_swap_page() would do when trying > to map a page obtained via the swapcache writable. > > As that logic is unnecessary, let's just remove it, removing the last > user of reuse_swap_page(). Thanks for cleaning this up. I didn't spot anything wrong. You could add Reviewed-by: Yang Shi > > Signed-off-by: David Hildenbrand > --- > include/trace/events/huge_memory.h | 1 - > mm/khugepaged.c | 11 ----------- > 2 files changed, 12 deletions(-) > > diff --git a/include/trace/events/huge_memory.h b/include/trace/events/huge_memory.h > index 4fdb14a81108..d651f3437367 100644 > --- a/include/trace/events/huge_memory.h > +++ b/include/trace/events/huge_memory.h > @@ -29,7 +29,6 @@ > EM( SCAN_VMA_NULL, "vma_null") \ > EM( SCAN_VMA_CHECK, "vma_check_failed") \ > EM( SCAN_ADDRESS_RANGE, "not_suitable_address_range") \ > - EM( SCAN_SWAP_CACHE_PAGE, "page_swap_cache") \ > EM( SCAN_DEL_PAGE_LRU, "could_not_delete_page_from_lru")\ > EM( SCAN_ALLOC_HUGE_PAGE_FAIL, "alloc_huge_page_failed") \ > EM( SCAN_CGROUP_CHARGE_FAIL, "ccgroup_charge_failed") \ > diff --git a/mm/khugepaged.c b/mm/khugepaged.c > index 35f14d0a00a6..9da9325ab4d4 100644 > --- a/mm/khugepaged.c > +++ b/mm/khugepaged.c > @@ -45,7 +45,6 @@ enum scan_result { > SCAN_VMA_NULL, > SCAN_VMA_CHECK, > SCAN_ADDRESS_RANGE, > - SCAN_SWAP_CACHE_PAGE, > SCAN_DEL_PAGE_LRU, > SCAN_ALLOC_HUGE_PAGE_FAIL, > SCAN_CGROUP_CHARGE_FAIL, > @@ -682,16 +681,6 @@ static int __collapse_huge_page_isolate(struct vm_area_struct *vma, > result = SCAN_PAGE_COUNT; > goto out; > } > - if (!pte_write(pteval) && PageSwapCache(page) && > - !reuse_swap_page(page)) { > - /* > - * Page is in the swap cache and cannot be re-used. > - * It cannot be collapsed into a THP. > - */ > - unlock_page(page); > - result = SCAN_SWAP_CACHE_PAGE; > - goto out; > - } > > /* > * Isolate the page to avoid collapsing an hugepage > -- > 2.34.1 >