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bh=PTrG+mr+PdluSGweJxje7TrtnEwJCDyxTOe2OFhcWXc=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=o4yUqM6oVUNoacmu1wWtJ75bIma2UAQusUEEfSQDbnr8ycc7zG7TyurxZtbnKeUDL TBk0m9j3yOEq3SCIomqxKpY32xsyvhbqkrPwe5VQlKv+E3aJwxLOpEBLAV6uR+bF11 YU8vax5sSMXE2DBHdiUybWcvepUPAxhbNcBwPx+Q= Date: Tue, 18 Apr 2023 15:21:09 -0700 From: Andrew Morton To: Matthew Wilcox Cc: Vishal Moola , Peng Zhang , linux-mm@kvack.org, linux-kernel@vger.kernel.org, mike.kravetz@oracle.com, sidhartha.kumar@oracle.com, muchun.song@linux.dev, wangkefeng.wang@huawei.com, sunnanyong@huawei.com Subject: Re: [PATCH v5 3/6] userfaultfd: convert copy_huge_page_from_user() to copy_folio_from_user() Message-Id: <20230418152109.32a90ebecc905ae60e2d072f@linux-foundation.org> In-Reply-To: References: <20230331093937.945725-1-zhangpeng362@huawei.com> <20230331093937.945725-4-zhangpeng362@huawei.com> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 1CAFA100013 X-Stat-Signature: 4hkw3ueyyo9da47tic7t81a146nc1iwj X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1681856471-29699 X-HE-Meta: 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 uGKkaRYf 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 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, 11 Apr 2023 04:40:17 +0100 Matthew Wilcox wrote: > On Thu, Apr 06, 2023 at 07:28:44PM -0700, Vishal Moola wrote: > > > - flush_dcache_page(subpage); > > > - > > > cond_resched(); > > > } > > > + flush_dcache_folio(dst_folio); > > > return ret_val; > > > } > > > > Moving the flush_dcache_page() outside the loop to be > > flush_dcache_folio() changes the behavior of the function. > > > > Initially, if it fails to copy the entire page, the function breaks out > > of the loop and returns the number of unwritten bytes without > > flushing the page from the cache. Now if it fails, it will still flush > > out the page it failed on, as well as any later pages it may not > > have gotten to yet. > > I'm not sure this is worth worrying about. Failing to copy the entire > folio is unlikely, and if we do, flushing the entire folio instead of just > a few pages in it is harmless. Plus I have patches which significantly > optiise flush_dcache_folio() over flush_dcache_page() (for the majority > of architectures) and so I think this change is actually beneficial in > the long term. Thanks, I'll send the series in for the next merge window as-is. If others remain unhappy with the flushing issue, please propose something during the next -rc cycle.