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[209.85.220.65]) by mx.google.com with SMTPS id j6sor2062055iog.11.2019.07.03.09.39.49 for (Google Transport Security); Wed, 03 Jul 2019 09:39:49 -0700 (PDT) Received-SPF: pass (google.com: domain of henryburns@google.com designates 209.85.220.65 as permitted sender) client-ip=209.85.220.65; Authentication-Results: mx.google.com; dkim=pass header.i=@google.com header.s=20161025 header.b="NqaumRs/"; spf=pass (google.com: domain of henryburns@google.com designates 209.85.220.65 as permitted sender) smtp.mailfrom=henryburns@google.com; dmarc=pass (p=REJECT sp=REJECT dis=NONE) header.from=google.com DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=kbDcTo4F8dXvZfSLbaTtza62bmr8qH9H1r6LEOl+lHU=; b=NqaumRs/9r4N+LLQZVW7EKfaaKJYqiFXNQS0FREyFBH2dA5dQe+xDeHSF8h0f4HvVD ZpP8PimJIp+5sU4npv4xahYwMV9fygG58x2bwWCGYHMgA8d9jsiTXdEjgjXy50uJ8PsW TEbw48ERxWv8d1V3mw3vCrwh3vLxHeL0fTrQR+MYMu9XRa8KDsArTcgvh9andjUd2RP+ 5woe4LfbhzoeKMgNBcJVBChrKTb8DDZ1RbCyrhk++x3Je98AMpNOduXga2w48ITbLxqT 5lCWRmkcHTJKIQBXr5u7Wu9Iwq41eXIyXnTqbszIjP3xokx9W176FvHXk2RhCqMaUmCV qGzw== X-Google-Smtp-Source: APXvYqzQyMYWqIT3Qfzpzptk3frJruzBTwW4rOb6aZvmElpX2SgWPwSUu0Enx4gwy/J+gJai0zJoUGBZgjWzPFk+Uh8= X-Received: by 2002:a5d:81c6:: with SMTP id t6mr15956036iol.86.1562171988733; Wed, 03 Jul 2019 09:39:48 -0700 (PDT) MIME-Version: 1.0 References: <20190702005122.41036-1-henryburns@google.com> <20190702141930.e31bf1c07a77514d976ef6e2@linux-foundation.org> <20190702152409.21c6c3787d125d61fb47840a@linux-foundation.org> In-Reply-To: From: Henry Burns Date: Wed, 3 Jul 2019 09:39:12 -0700 Message-ID: Subject: Re: [PATCH v2] mm/z3fold.c: Lock z3fold page before __SetPageMovable() To: Vitaly Wool Cc: Andrew Morton , Shakeel Butt , Vitaly Vul , Mike Rapoport , Xidong Wang , Jonathan Adams , Linux MM , LKML Content-Type: text/plain; charset="UTF-8" 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, Jul 2, 2019 at 10:54 PM Vitaly Wool wrote: > > On Wed, Jul 3, 2019 at 12:24 AM Andrew Morton wrote: > > > > On Tue, 2 Jul 2019 15:17:47 -0700 Henry Burns wrote: > > > > > > > > > + if (can_sleep) { > > > > > > > + lock_page(page); > > > > > > > + __SetPageMovable(page, pool->inode->i_mapping); > > > > > > > + unlock_page(page); > > > > > > > + } else { > > > > > > > + if (!WARN_ON(!trylock_page(page))) { > > > > > > > + __SetPageMovable(page, pool->inode->i_mapping); > > > > > > > + unlock_page(page); > > > > > > > + } else { > > > > > > > + pr_err("Newly allocated z3fold page is locked\n"); > > > > > > > + WARN_ON(1); > > > > The WARN_ON will have already warned in this case. > > > > But the whole idea of warning in this case may be undesirable. We KNOW > > that the warning will sometimes trigger (yes?). So what's the point in > > scaring users? > > Well, normally a newly allocated page that we own should not be locked > by someone else so this is worth a warning IMO. With that said, the > else branch here appears to be redundant. The else branch has been removed, and I think it's possible (albeit unlikely) that the trylock could fail due to either compaction or kstaled (In which case the page just won't be movable). Also Vitaly, do you have a preference between the two emails? I'm not sure which one to include.