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[211.29.132.246]) by mx.google.com with ESMTP id q9si53897563pfl.287.2019.08.06.14.22.56 for ; Tue, 06 Aug 2019 14:22:56 -0700 (PDT) Received-SPF: neutral (google.com: 211.29.132.246 is neither permitted nor denied by best guess record for domain of david@fromorbit.com) client-ip=211.29.132.246; Authentication-Results: mx.google.com; spf=neutral (google.com: 211.29.132.246 is neither permitted nor denied by best guess record for domain of david@fromorbit.com) smtp.mailfrom=david@fromorbit.com Received: from dread.disaster.area (pa49-181-167-148.pa.nsw.optusnet.com.au [49.181.167.148]) by mail104.syd.optusnet.com.au (Postfix) with ESMTPS id 7490B43C5F0; Wed, 7 Aug 2019 07:22:55 +1000 (AEST) Received: from dave by dread.disaster.area with local (Exim 4.92) (envelope-from ) id 1hv6tw-000533-Gl; Wed, 07 Aug 2019 07:21:48 +1000 Date: Wed, 7 Aug 2019 07:21:48 +1000 From: Dave Chinner To: Brian Foster Cc: linux-xfs@vger.kernel.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org Subject: Re: [PATCH 15/24] xfs: eagerly free shadow buffers to reduce CIL footprint Message-ID: <20190806212148.GH7777@dread.disaster.area> References: <20190801021752.4986-1-david@fromorbit.com> <20190801021752.4986-16-david@fromorbit.com> <20190805180300.GE14760@bfoster> <20190805233326.GA7777@dread.disaster.area> <20190806125727.GD2979@bfoster> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190806125727.GD2979@bfoster> User-Agent: Mutt/1.10.1 (2018-07-13) X-Optus-CM-Score: 0 X-Optus-CM-Analysis: v=2.2 cv=P6RKvmIu c=1 sm=1 tr=0 cx=a_idp_d a=gu9DDhuZhshYSb5Zs/lkOA==:117 a=gu9DDhuZhshYSb5Zs/lkOA==:17 a=jpOVt7BSZ2e4Z31A5e1TngXxSK0=:19 a=kj9zAlcOel0A:10 a=FmdZ9Uzk2mMA:10 a=7-415B0cAAAA:8 a=b5DoXVf_MhzvH81YMsoA:9 a=CjuIK1q_8ugA:10 a=biEYGPWJfzWAr4FL6Ov7:22 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, Aug 06, 2019 at 08:57:27AM -0400, Brian Foster wrote: > On Tue, Aug 06, 2019 at 09:33:26AM +1000, Dave Chinner wrote: > > I'll recheck this, but I'm pretty sure overwrite won't leave a > > shadow buffer around. > > > > But before that we have the following logic: > > static void > xlog_cil_alloc_shadow_bufs( > ... > > if (!lip->li_lv_shadow || > buf_size > lip->li_lv_shadow->lv_size) { > ... > lv = kmem_alloc_large(buf_size, KM_SLEEP | KM_NOFS); > ... > lip->li_lv_shadow = lv; > } else { > > } > ... > } > > ... which always allocates a shadow buffer if one doesn't exist. We > don't look at the currently used (lip->li_lv) buffer at all here. IIUC, > that has to do with the TOCTOU race described in the big comment above > the function.. hm? You might be right there. I haven't had a chance to follow up on this from yesterday yet, so I'll keep this in mind when I look at it again. Cheers, Dave. -- Dave Chinner david@fromorbit.com