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[23.128.96.18]) by mx.google.com with ESMTP id p9si19420309iov.92.2021.05.25.16.03.47; Tue, 25 May 2021 16:04:00 -0700 (PDT) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18; Authentication-Results: mx.google.com; dkim=pass header.i=@gmail.com header.s=20161025 header.b=bMJQAdgE; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=NONE sp=QUARANTINE dis=NONE) header.from=gmail.com Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231148AbhEYWfA (ORCPT + 99 others); Tue, 25 May 2021 18:35:00 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43986 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230202AbhEYWe7 (ORCPT ); Tue, 25 May 2021 18:34:59 -0400 Received: from mail-ed1-x531.google.com (mail-ed1-x531.google.com [IPv6:2a00:1450:4864:20::531]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B36D4C061574 for ; Tue, 25 May 2021 15:33:28 -0700 (PDT) Received: by mail-ed1-x531.google.com with SMTP id w12so30362852edx.1 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=QMmpE6zxvJzW0J3LGe9pyK8qo0WLak2be2zcpTd7GFQCMgrHgExpHRNKlJ4tJu7SFI 1B02c/nY4YE2O5EHOYtaFOYeVP0J33ng8K9Y6+Wy0ySrhm1vb2omXKNLhZ8MfrOb5dSV 1FtrbxxmpvmxqE/d8F/vnRS2SbKYvK2S7aOBH9figH5/YbUSDqBsnyDjwW5e+25Ko6sR ujIgp56c/Gk85YvCjJI+W+jGObSkSR6KPTlYDj/zKdCnWQWMdpmEq4HHJBwZ7Had7Bck EdeaAyBjfpQk0C71xA/cIM6JKbqLNjQHMEPZ5h9+iqHre9AsohnQtExSf4ULAi5ig5ma 1BSQ== X-Gm-Message-State: AOAM531xKVaUy4T08OE9P6rPlnP66LjDiw8tZ2vLgG4t3G+fPIV8N8g7 nIT+ZOi0xjy0cX+XLO8d7ht994JmE/J7vsL8riA= 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" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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