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[77.136.42.76]) by smtp.gmail.com with ESMTPSA id f130sm11705291wme.41.2018.12.17.06.42.54 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 17 Dec 2018 06:42:54 -0800 (PST) Subject: Re: [PATCH] iov_iter: optimize page_copy_sane() To: Eric Dumazet , linux-kernel Cc: Eric Dumazet , Al Viro References: <20181208133735.245799-1-edumazet@google.com> From: Eric Dumazet Message-ID: <0d6058b9-8123-6d8c-0571-6ea9a5cd822d@gmail.com> Date: Mon, 17 Dec 2018 06:42:50 -0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: <20181208133735.245799-1-edumazet@google.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 12/08/2018 05:37 AM, Eric Dumazet wrote: > Avoid cache line miss dereferencing struct page if we can. > > page_copy_sane() mostly deals with order-0 pages. > > Signed-off-by: Eric Dumazet > Cc: Al Viro > --- > lib/iov_iter.c | 14 ++++++++++++-- > 1 file changed, 12 insertions(+), 2 deletions(-) > > diff --git a/lib/iov_iter.c b/lib/iov_iter.c > index 54c248526b55fc498c996f2a5ea651262fcc7f61..2a1e282c3d38e2d03b075f54b7f9313e48b90289 100644 > --- a/lib/iov_iter.c > +++ b/lib/iov_iter.c > @@ -854,8 +854,18 @@ EXPORT_SYMBOL(_copy_from_iter_full_nocache); > > static inline bool page_copy_sane(struct page *page, size_t offset, size_t n) > { > - struct page *head = compound_head(page); > - size_t v = n + offset + page_address(page) - page_address(head); > + struct page *head; > + size_t v = n + offset; > + > + /* > + * Fast path if this is an order-0 page, > + * or if the copied area fits the first page of a compound one. > + */ > + if (likely(n <= v && v <= PAGE_SIZE)) > + return true; > + > + head = compound_head(page); > + v += (page - head) << PAGE_SHIFT; > > if (likely(n <= v && v <= (PAGE_SIZE << compound_order(head)))) > return true; > Hi Alexander ! Any news on this patch ? Thanks !