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[172.10.233.147]) by smtp.gmail.com with ESMTPSA id bs42-20020a05620a472a00b006b61b2cb1d2sm9741158qkb.46.2022.11.22.01.13.40 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 22 Nov 2022 01:13:42 -0800 (PST) Date: Tue, 22 Nov 2022 01:13:39 -0800 (PST) From: Hugh Dickins X-X-Sender: hugh@ripple.attlocal.net To: "Kirill A. Shutemov" cc: Hugh Dickins , Andrew Morton , Yu Zhao , Linus Torvalds , Johannes Weiner , Matthew Wilcox , David Hildenbrand , Vlastimil Babka , Peter Xu , Yang Shi , John Hubbard , Mike Kravetz , Sidhartha Kumar , Muchun Song , Miaohe Lin , Naoya Horiguchi , Mina Almasry , James Houghton , Zach O'Keefe , linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH 1/3 fix] mm,thp,rmap: subpages_mapcount of PTE-mapped subpages: fix In-Reply-To: <20221121123812.4sxk7ewzfhdqq6zs@box.shutemov.name> Message-ID: <536d9a99-1cbb-d05d-21bf-4cc8d032692@google.com> References: <5f52de70-975-e94f-f141-543765736181@google.com> <78fa518-85b5-32c0-ee92-537fa46131f6@google.com> <759077a6-a08-5bb0-a0b6-53be2fe8b56a@google.com> <7a4f5e5e-de33-dace-c526-4a3d3cf5f6e0@google.com> <20221121123812.4sxk7ewzfhdqq6zs@box.shutemov.name> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1669108424; a=rsa-sha256; cv=none; b=Q4Oyty8NGIRcfgllGNZWMlqFFXrMOZYzwk1HIPMMTWBHGefKH3xt8eZy4BlLCsRfU3JocB eC+nVRygXgP2m2rZJv8cUBv3XnC6R/iGr9Km+zWJRJ/XOW6jxAa3vE+jlX9XnMm20x0CDz dmef7pyZekUYZcP7Jb4EqfyEZk0vIQc= ARC-Authentication-Results: i=1; imf21.hostedemail.com; dkim=pass header.d=google.com header.s=20210112 header.b=O+mOhBKw; dmarc=pass (policy=reject) header.from=google.com; spf=pass (imf21.hostedemail.com: domain of hughd@google.com designates 209.85.222.175 as permitted sender) smtp.mailfrom=hughd@google.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1669108424; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=7xqdWpmMgK4TlDGSJjLz9IABXgjJRE62xPUxcQSf0wk=; b=1dvqt1fFiZE/HFIzhS3ThEkzeMIQQ6KsnA3e3YHhBF+/PjPGr5tBhZvrQ15K5jY9gPfjro 0bhSR3EoETm6+lSaUpxpEL2HlUrzv4VgfbXR7zuPkenHJHsVffLmRrRwUCvvqXFhflgIs0 XGnkhdTEPg5U6572gwJ0fqxFbmxWXq0= Authentication-Results: imf21.hostedemail.com; dkim=pass header.d=google.com header.s=20210112 header.b=O+mOhBKw; dmarc=pass (policy=reject) header.from=google.com; spf=pass (imf21.hostedemail.com: domain of hughd@google.com designates 209.85.222.175 as permitted sender) smtp.mailfrom=hughd@google.com X-Stat-Signature: tncds7on443pgusichgnapjqgdc9cbpr X-Rspamd-Queue-Id: 524281C0002 X-Rspam-User: X-Rspamd-Server: rspam11 X-HE-Tag: 1669108424-874377 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, 21 Nov 2022, Kirill A. Shutemov wrote: > On Fri, Nov 18, 2022 at 05:35:05PM -0800, Hugh Dickins wrote: ... > > --- a/mm/rmap.c > > +++ b/mm/rmap.c > > @@ -1281,7 +1281,7 @@ void page_add_anon_rmap(struct page *page, > > struct compound_mapcounts mapcounts; > > int nr = 0, nr_pmdmapped = 0; > > bool compound = flags & RMAP_COMPOUND; > > - bool first; > > + bool first = true; > > > > if (unlikely(PageKsm(page))) > > lock_page_memcg(page); > > Other option is to drop PageTransHuge() check that you already claim to be > redundant. > > Or have else BUG() to catch cases where the helper called with > compound=true on non-THP page. I'm sticking with the "first = true". I did receive a report of bloating some tiny config a little, on the very first series, so I've been on guard since then about adding THP code where the optimizer cannot see to remove it: so do want to keep the PageTransHuge check in there. Could be done in other ways, yes, but I'd ended up feeling this was the best compromise. Hugh