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=ham 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 A2878C2B9F8 for ; Tue, 25 May 2021 17:07:20 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 3BFC66141C for ; Tue, 25 May 2021 17:07:20 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 3BFC66141C 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 9CD3A6B0070; Tue, 25 May 2021 13:07:19 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 9A4B46B0071; Tue, 25 May 2021 13:07:19 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 86CD36B0072; Tue, 25 May 2021 13:07:19 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0240.hostedemail.com [216.40.44.240]) by kanga.kvack.org (Postfix) with ESMTP id 53D046B0070 for ; Tue, 25 May 2021 13:07:19 -0400 (EDT) Received: from smtpin14.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with ESMTP id D23899880 for ; Tue, 25 May 2021 17:07:18 +0000 (UTC) X-FDA: 78180384156.14.88D2869 Received: from mail-ej1-f44.google.com (mail-ej1-f44.google.com [209.85.218.44]) by imf23.hostedemail.com (Postfix) with ESMTP id 30374A0001D7 for ; Tue, 25 May 2021 17:07:13 +0000 (UTC) Received: by mail-ej1-f44.google.com with SMTP id s22so48262994ejv.12 for ; Tue, 25 May 2021 10:07:18 -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=shX5o7fX3QC1vBrjY1MAQkvRCh6xIuYlJU65dj3inTo=; b=EZx5bOBS1D3lFTJnRSsg224irnopnZIFuU9EIi23AcWgi3puLB8NM/RhYBvXIcyv3T 5w+Z/FOTRJX1ibduGD4k2I0l0xDoYtM2NgWwpFwBo2XMsIQeBrS3NDlzHgF0/aXSpXt8 1cTPMTfNJc9SAr2oN/cE1Ndhc6EUrLQIVcVYoN4ofOU402PhFMQY1PHgnt6Cgp4gBdqM pZgLZbznGnOEYHvN1s21/soP/HcdRNp6jsOpP3AH9mDdJVjBOhz5k4e5zp8HtWYljhFK Ip3h4YvpqZfTh8HATErqgSa9gaabPyTeKjmZTBbU5D9JNQLHiPFGBJPZhu+orzVn8tjh dgVg== 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=shX5o7fX3QC1vBrjY1MAQkvRCh6xIuYlJU65dj3inTo=; b=cfwZ/mjbSf5Edvrm/k8sds28bLVth6M7kAUVyGMxI/eutBNSieylhTSLHeVtHmD309 7cOF3ay2bL9/923MPmNw1iEdSfZfkuqz1KHPw0K3h4+01HXDFEZ8ynegUPLtwgPe9ZKI cjKIm66c/fo8wJAE97ide/M+cHXE9GXyEBrc3tOdEzqJRVbs1UvTdhQ2Ske/3Z2ErKr9 b27w9ooqe7p2BHEPbVZWdEeajJItiMIqJbrVY3KMBvkiVDNWkNHJT6lSJJCbY/gCPTha vPutPslF1/+xO/x17C9OqzxmoiBZKX7Y4IPXOSGJDJeQ/QjtaPuJ56LSyRugOn82a9Fr xWgQ== X-Gm-Message-State: AOAM532MfIxCiizFHH5zfsy/JpHY8+Wr1i6psfR0ErL243xHxgrbiuMZ YBpsscaFWfu+2RQjObnF20qTjIYuwdPspvx9QAY= X-Google-Smtp-Source: ABdhPJwf9CiiGaJWdMqwlVDs9Mk0UOGu6dNQmIVUXJqjoqUuy4s3sORqO7ENhE2AE8f8SG0F1GFLXf9GvPoXDEmUphM= X-Received: by 2002:a17:906:1699:: with SMTP id s25mr29258812ejd.238.1621962437398; Tue, 25 May 2021 10:07:17 -0700 (PDT) MIME-Version: 1.0 References: <20210525162145.3510-1-shy828301@gmail.com> In-Reply-To: From: Yang Shi Date: Tue, 25 May 2021 10:07:05 -0700 Message-ID: Subject: Re: [v3 PATCH 1/2] mm: rmap: make try_to_unmap() void function To: Minchan Kim Cc: Hugh Dickins , 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" Authentication-Results: imf23.hostedemail.com; dkim=pass header.d=gmail.com header.s=20161025 header.b=EZx5bOBS; dmarc=pass (policy=none) header.from=gmail.com; spf=pass (imf23.hostedemail.com: domain of shy828301@gmail.com designates 209.85.218.44 as permitted sender) smtp.mailfrom=shy828301@gmail.com X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 30374A0001D7 X-Stat-Signature: h5uunj7npa1ocod8h1fnmjyxcwh3jugj X-HE-Tag: 1621962433-290028 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 9:46 AM Minchan Kim wrote: > > On Tue, May 25, 2021 at 09:21:44AM -0700, 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 > > --- > > 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; > > Couldn't we use page_mapped instead of page_mapcount here? Yes, of course. Actually this has been discussed in v2 review. Most (or half) callers actually don't check the return value of try_to_unmap() except hwpoison, vmscan and THP split. It sounds suboptimal to have everyone pay the cost. So I thought Hugh's suggestion made sense to me. Quoted the discussion below: > @@ -1777,7 +1779,7 @@ bool try_to_unmap(struct page *page, enum ttu_flags flags) > else > rmap_walk(page, &rwc); > > - return !page_mapcount(page) ? true : false; > + return !total_mapcount(page) ? true : false; That always made me wince: "return !total_mapcount(page);" surely. Or slightly better, "return !page_mapped(page);", since at least that one breaks out as soon as it sees a mapcount. Though I guess I'm being silly there, since that case should never occur, so both total_mapcount() and page_mapped() scan through all pages. Or better, change try_to_unmap() to void: most callers ignore its return value anyway, and make their own decisions; the remaining few could be changed to do the same. Though again, I may be being silly, since the expensive THP case is not the common case. > With boolean return of try sematic looks reasonable to me > rather than void. > > > } > > > > /** > > 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 > > > >