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=-12.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 844B8C47086 for ; Tue, 25 May 2021 22:33:31 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 2187661409 for ; Tue, 25 May 2021 22:33:31 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 2187661409 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=gmail.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id ED4F66B0036; Tue, 25 May 2021 18:33:29 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id E8A846B006C; Tue, 25 May 2021 18:33:29 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 978D06B006E; Tue, 25 May 2021 18:33:29 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0073.hostedemail.com [216.40.44.73]) by kanga.kvack.org (Postfix) with ESMTP id 1A1C96B0036 for ; Tue, 25 May 2021 18:33:29 -0400 (EDT) Received: from smtpin12.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay03.hostedemail.com (Postfix) with ESMTP id AABEA8249980 for ; Tue, 25 May 2021 22:33:28 +0000 (UTC) X-FDA: 78181206096.12.DDA819A Received: from mail-ed1-f41.google.com (mail-ed1-f41.google.com [209.85.208.41]) by imf09.hostedemail.com (Postfix) with ESMTP id 691ED6000258 for ; Tue, 25 May 2021 22:33:24 +0000 (UTC) Received: by mail-ed1-f41.google.com with SMTP id h16so38093877edr.6 for ; Tue, 25 May 2021 15:33:28 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=YUMO4ev2fi5whCBLny3igBaOoEj6ePRUeQXInqjVyNM=; b=bMJQAdgEryq0sPrbnNCe5x4cW0/jeT0J+TPAw+SA1Q5+6Ip4Sa5uFnkjbLgvhCKv12 Qyi58CtPHjUo2xpfMWhudlnhGllCbulR19B2WMyD51nx9Q2v3/YdjGLVp3E2sTj2H/P3 awqap4IPUFcusb6NaWIkagP62xFuXWZkYF7uYe3yGlFdMVHjXCR8hyEVbANPZgtMjUuY vmmSH5gQ8C7jL0doqSCz0gBnNysDbevvH+MncG8wGQkzPdcgEBhjOzA3Udn+1dZvjoXT NIPL1WSERKHaklDXlWC5x+k4bkR2zQF0sWZvsxiPElNx8X2oDyNQmcMZ8zYxn4HsyNpM X2IQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=YUMO4ev2fi5whCBLny3igBaOoEj6ePRUeQXInqjVyNM=; b=Vw+1Hmb+z6LzUlLw74LjrAHKKgeve3WADxIqcq71LtkvRZDERgjSdNhtCtmD6G4Lcj weaOY71C9W/jppuHW5T5ikqYSMH82zfSbl/hEHhcKMIFtlnGyqPoot9oPF9HRh7aH12k hN3OKV+be14NAf7WMDLM9ZQGrQWGvP6m4J6+IkkGofEWXbj69K5AF9oBOB39y6WJ4v6u MGdIoOea7HVv1HUbDOI5walumdG/UYjPRaKzjam2DNtfr96MMA8Nf/WG4dSdCXad9nA6 NJqN0caxFQgb2RGQoGASnSFwTC6m/4M+3nx1lsHwsJWzC9t6feaUVEFPve9QxuelUkY8 fCIw== X-Gm-Message-State: AOAM533FUnxLU+vzHQZp8GPfCmOCGnJ2y8hVXvU+uPhuxejrhwxjCada 6vA85EtlvusBmlVyg70n2Zl9PjQQcFSN2zGIlh3s6fi3GAQ= X-Google-Smtp-Source: ABdhPJyQoa9JICY+XRJRIYukmQB8d441BozFXAbEKiu5+PHyTIFgN1TXmc2XlOMyDEurOdMnyYqW4O29uqc1CY6CZqw= X-Received: by 2002:a05:6402:1052:: with SMTP id e18mr35201690edu.366.1621982007211; Tue, 25 May 2021 15:33:27 -0700 (PDT) MIME-Version: 1.0 References: <20210525162145.3510-1-shy828301@gmail.com> In-Reply-To: From: Yang Shi Date: Tue, 25 May 2021 15:33:15 -0700 Message-ID: Subject: Re: [v3 PATCH 1/2] mm: rmap: make try_to_unmap() void function To: Hugh Dickins Cc: Zi Yan , "Kirill A. Shutemov" , =?UTF-8?B?SE9SSUdVQ0hJIE5BT1lBKOWggOWPoyDnm7TkuZ8p?= , Wang Yugui , Andrew Morton , Linux MM , Linux Kernel Mailing List Content-Type: text/plain; charset="UTF-8" X-Rspamd-Queue-Id: 691ED6000258 Authentication-Results: imf09.hostedemail.com; dkim=pass header.d=gmail.com header.s=20161025 header.b=bMJQAdgE; spf=pass (imf09.hostedemail.com: domain of shy828301@gmail.com designates 209.85.208.41 as permitted sender) smtp.mailfrom=shy828301@gmail.com; dmarc=pass (policy=none) header.from=gmail.com X-Rspamd-Server: rspam04 X-Stat-Signature: eei9764n56xcxra49ri5tuksygmfnscu X-HE-Tag: 1621982004-39215 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 Tue, May 25, 2021 at 2:12 PM Hugh Dickins wrote: > > On Tue, 25 May 2021, Yang Shi wrote: > > > Currently try_to_unmap() return bool value by checking page_mapcount(), > > however this may return false positive since page_mapcount() doesn't > > check all subpages of compound page. The total_mapcount() could be used > > instead, but its cost is higher since it traverses all subpages. > > > > Actually the most callers of try_to_unmap() don't care about the > > return value at all. So just need check if page is still mapped by > > page_mapped() when necessary. And page_mapped() does bail out early > > when it finds mapped subpage. > > > > Suggested-by: Hugh Dickins > > Signed-off-by: Yang Shi > > Thanks for doing this, I like it, you can add > Acked-by: Hugh Dickins Thank you. > > Let's all ignore checkpatch's complaint on "struct page *": > that try_to_unmap() prototype is consistent with others in rmap.h, > and changing them to "struct page *page" adds no information at all. > > But a nit in mm/memory-failure.c: unmap_success no longer needs > to be initialized to true on entry to hwpoison_user_mappings(). Will fix it. > > More seriously, I question the ordering of the two patches: > I think this 1/2 should be 2/2, and the other be 1/2. The other is > the one which replaces a BUG by a WARN, which will be wanted Cc stable; > whereas this one is really just a cleanup - I don't think there's a > serious consequence from the faint possibility of wrong unmap_success > on THP, in either memory-failure.c or vmscan.c - wrong message, wrong > stats, but more than that? And memory-failure.c on THP somewhat a > work in progress IIUC. > > Unfortunately, they can't just be swapped but need rediffing. > Or do you disagree that's a better ordering? No, I don't. Will reorder them in the next version, anyway I need to fix something. > > As it stands, I imagine my series of THP unmap fixes (most needing Cc > stable) coming on top of your "mm: thp: check page_mapped instead of > page_mapcount for split" (umm, that's a bad title), but before this > cleanup. > > Though I'm responding before I've looked through the stable trees: > it's not of overriding importance, but I'll want to try to minimize > the number of patches that need redoing for older stables, which might > affect the ordering. (And it might end up easiest if I bring your two > patches into my series, then ask Andrew to replace.) > > Further complicated by Andrew having brought in the nouveau reorg of > mm/rmap.c (oh, and that touches mm/huge_memory.c unmap_page() too). > I expect I'll have to send Andrew a series to go before all that, > together with fixups to that to sit on top of it. Sigh. Well, > we can only blame me for not getting those THP fixes in sooner. > > Hugh > > > --- > > include/linux/rmap.h | 2 +- > > mm/huge_memory.c | 4 +--- > > mm/memory-failure.c | 13 ++++++------- > > mm/rmap.c | 6 +----- > > mm/vmscan.c | 3 ++- > > 5 files changed, 11 insertions(+), 17 deletions(-) > > > > diff --git a/include/linux/rmap.h b/include/linux/rmap.h > > index def5c62c93b3..116cb193110a 100644 > > --- a/include/linux/rmap.h > > +++ b/include/linux/rmap.h > > @@ -194,7 +194,7 @@ static inline void page_dup_rmap(struct page *page, bool compound) > > int page_referenced(struct page *, int is_locked, > > struct mem_cgroup *memcg, unsigned long *vm_flags); > > > > -bool try_to_unmap(struct page *, enum ttu_flags flags); > > +void try_to_unmap(struct page *, enum ttu_flags flags); > > > > /* Avoid racy checks */ > > #define PVMW_SYNC (1 << 0) > > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > > index 19195fca1aee..80fe642d742d 100644 > > --- a/mm/huge_memory.c > > +++ b/mm/huge_memory.c > > @@ -2336,15 +2336,13 @@ static void unmap_page(struct page *page) > > { > > enum ttu_flags ttu_flags = TTU_IGNORE_MLOCK | > > TTU_RMAP_LOCKED | TTU_SPLIT_HUGE_PMD; > > - bool unmap_success; > > > > VM_BUG_ON_PAGE(!PageHead(page), page); > > > > if (PageAnon(page)) > > ttu_flags |= TTU_SPLIT_FREEZE; > > > > - unmap_success = try_to_unmap(page, ttu_flags); > > - VM_BUG_ON_PAGE(!unmap_success, page); > > + try_to_unmap(page, ttu_flags); > > } > > > > static void remap_page(struct page *page, unsigned int nr) > > diff --git a/mm/memory-failure.c b/mm/memory-failure.c > > index 9dcc9bcea731..6dd53ff34825 100644 > > --- a/mm/memory-failure.c > > +++ b/mm/memory-failure.c > > @@ -1126,7 +1126,7 @@ static bool hwpoison_user_mappings(struct page *p, unsigned long pfn, > > collect_procs(hpage, &tokill, flags & MF_ACTION_REQUIRED); > > > > if (!PageHuge(hpage)) { > > - unmap_success = try_to_unmap(hpage, ttu); > > + try_to_unmap(hpage, ttu); > > } else { > > if (!PageAnon(hpage)) { > > /* > > @@ -1138,17 +1138,16 @@ static bool hwpoison_user_mappings(struct page *p, unsigned long pfn, > > */ > > mapping = hugetlb_page_mapping_lock_write(hpage); > > if (mapping) { > > - unmap_success = try_to_unmap(hpage, > > - ttu|TTU_RMAP_LOCKED); > > + try_to_unmap(hpage, ttu|TTU_RMAP_LOCKED); > > i_mmap_unlock_write(mapping); > > - } else { > > + } else > > pr_info("Memory failure: %#lx: could not lock mapping for mapped huge page\n", pfn); > > - unmap_success = false; > > - } > > } else { > > - unmap_success = try_to_unmap(hpage, ttu); > > + try_to_unmap(hpage, ttu); > > } > > } > > + > > + unmap_success = !page_mapped(hpage); > > if (!unmap_success) > > pr_err("Memory failure: %#lx: failed to unmap page (mapcount=%d)\n", > > pfn, page_mapcount(hpage)); > > diff --git a/mm/rmap.c b/mm/rmap.c > > index a35cbbbded0d..728de421e43a 100644 > > --- a/mm/rmap.c > > +++ b/mm/rmap.c > > @@ -1748,10 +1748,8 @@ static int page_not_mapped(struct page *page) > > * > > * Tries to remove all the page table entries which are mapping this > > * page, used in the pageout path. Caller must hold the page lock. > > - * > > - * If unmap is successful, return true. Otherwise, false. > > */ > > -bool try_to_unmap(struct page *page, enum ttu_flags flags) > > +void try_to_unmap(struct page *page, enum ttu_flags flags) > > { > > struct rmap_walk_control rwc = { > > .rmap_one = try_to_unmap_one, > > @@ -1776,8 +1774,6 @@ bool try_to_unmap(struct page *page, enum ttu_flags flags) > > rmap_walk_locked(page, &rwc); > > else > > rmap_walk(page, &rwc); > > - > > - return !page_mapcount(page) ? true : false; > > } > > > > /** > > diff --git a/mm/vmscan.c b/mm/vmscan.c > > index f96d62159720..fa5052ace415 100644 > > --- a/mm/vmscan.c > > +++ b/mm/vmscan.c > > @@ -1499,7 +1499,8 @@ static unsigned int shrink_page_list(struct list_head *page_list, > > if (unlikely(PageTransHuge(page))) > > flags |= TTU_SPLIT_HUGE_PMD; > > > > - if (!try_to_unmap(page, flags)) { > > + try_to_unmap(page, flags); > > + if (page_mapped(page)) { > > stat->nr_unmap_fail += nr_pages; > > if (!was_swapbacked && PageSwapBacked(page)) > > stat->nr_lazyfree_fail += nr_pages; > > -- > > 2.26.2