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Received: from willy by casper.infradead.org with local (Exim 4.94.2 #2 (Red Hat Linux)) id 1pm4rh-005H4G-Tg; Tue, 11 Apr 2023 03:40:17 +0000 Date: Tue, 11 Apr 2023 04:40:17 +0100 From: Matthew Wilcox To: Vishal Moola Cc: Peng Zhang , linux-mm@kvack.org, linux-kernel@vger.kernel.org, akpm@linux-foundation.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: References: <20230331093937.945725-1-zhangpeng362@huawei.com> <20230331093937.945725-4-zhangpeng362@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: C07CB100008 X-Stat-Signature: 7ojsb36m55hcfotx1bzx4n71hq4qzfoj X-HE-Tag: 1681184428-726798 X-HE-Meta: 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 Tf30Ndab gQTBhmsTrV8FnRfuchSJVt0a2y83ifYbbz2Jt0F3ezVcbgjaSvinFFJS7yYQ3sWVvrtl1ZDb93NmcBepU7LkRUtzrf+UJKJaum/rOwpIzSZw2rjkDkXWzoq3cSrmKmRMIsHs7j7z8lXLQNeyyfqX4VysrtgQm03SskZui5jPxWPHOrFowxf8NSms/utwF1dG3RS+WXAsoskMq0AukVPJ6JHUIDdq27fTwD4PWcHkj7N0sqbQQ1bAfKyuXWyCMASga6NWDIAxp9JcYKjkVXIHgI449zg== 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 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.