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Wed, 22 Mar 2023 06:17:31 -0400 X-MC-Unique: 6nORCHWmP_ua3bSCsrLsXw-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.rdu2.redhat.com [10.11.54.7]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id CED58185A790; Wed, 22 Mar 2023 10:17:30 +0000 (UTC) Received: from localhost (ovpn-13-195.pek2.redhat.com [10.72.13.195]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 9CA41140EBF4; Wed, 22 Mar 2023 10:17:29 +0000 (UTC) Date: Wed, 22 Mar 2023 18:17:25 +0800 From: Baoquan He To: Lorenzo Stoakes Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, Andrew Morton , Uladzislau Rezki , Matthew Wilcox , David Hildenbrand , Liu Shixin , Jiri Olsa , Jens Axboe , Alexander Viro Subject: Re: [PATCH v4 3/4] iov_iter: add copy_page_to_iter_atomic() Message-ID: References: <31482908634cbb68adafedb65f0b21888c194a1b.1679431886.git.lstoakes@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <31482908634cbb68adafedb65f0b21888c194a1b.1679431886.git.lstoakes@gmail.com> X-Scanned-By: MIMEDefang 3.1 on 10.11.54.7 X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: B5F52C0003 X-Stat-Signature: ih74no5q3dnjfdtot8s67kg63iy1aghe X-HE-Tag: 1679480257-842251 X-HE-Meta: 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 HdcCFYuQ 6TopvhOiBURpW22vTpKHckYReWwZ6XIUsifAILa1w3qmYgeDsXGf8MWD1ivOKUOO+NuJsV2DSsGQe1yyDpDuW6JpWEUQV/IoLgp16g9YF1lkMnWA0nJFFm0yi9k9eDlt2jTVUdU9jbVdF/SV0BOIWqXxQvTWD2s5DrVMDkq6gvxkQpEt9SJiJlNBqXay6rTGzMncz/26hQz71EbGz2qMmPWs7xQOnIss7PfyW2k780dEZUWVyioSqm86s19WP9qkEuCT1433Fh4IOHwVgfQD9Ce35qhqrMq/TSzl+ 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 03/21/23 at 08:54pm, Lorenzo Stoakes wrote: > Provide an atomic context equivalent for copy_page_to_iter(). This eschews > the might_fault() check copies memory in the same way that > copy_page_from_iter_atomic() does. > > This functions assumes a non-compound page, however this mimics the > existing behaviour of copy_page_from_iter_atomic(). I am keeping the > behaviour consistent between the two, deferring any such change to an > explicit folio-fication effort. > > This is being added in order that an iteratable form of vread() can be > implemented with known prefaulted pages to avoid the need for mutex > locking. > > Signed-off-by: Lorenzo Stoakes > --- > include/linux/uio.h | 2 ++ > lib/iov_iter.c | 28 ++++++++++++++++++++++++++++ > 2 files changed, 30 insertions(+) > > diff --git a/include/linux/uio.h b/include/linux/uio.h > index 27e3fd942960..fab07103090f 100644 > --- a/include/linux/uio.h > +++ b/include/linux/uio.h > @@ -154,6 +154,8 @@ static inline struct iovec iov_iter_iovec(const struct iov_iter *iter) > > size_t copy_page_from_iter_atomic(struct page *page, unsigned offset, > size_t bytes, struct iov_iter *i); > +size_t copy_page_to_iter_atomic(struct page *page, unsigned offset, > + size_t bytes, struct iov_iter *i); > void iov_iter_advance(struct iov_iter *i, size_t bytes); > void iov_iter_revert(struct iov_iter *i, size_t bytes); > size_t fault_in_iov_iter_readable(const struct iov_iter *i, size_t bytes); > diff --git a/lib/iov_iter.c b/lib/iov_iter.c > index 274014e4eafe..48ca1c5dfc04 100644 > --- a/lib/iov_iter.c > +++ b/lib/iov_iter.c > @@ -821,6 +821,34 @@ size_t copy_page_from_iter_atomic(struct page *page, unsigned offset, size_t byt > } > EXPORT_SYMBOL(copy_page_from_iter_atomic); > > +size_t copy_page_to_iter_atomic(struct page *page, unsigned offset, size_t bytes, > + struct iov_iter *i) > +{ > + char *kaddr = kmap_local_page(page); I am a little confused about the name of this new function. In its conterpart, copy_page_from_iter_atomic(), kmap_atomic()/kunmpa_atomic() are used. With them, if CONFIG_HIGHMEM=n, it's like below: static inline void *kmap_atomic(struct page *page) { if (IS_ENABLED(CONFIG_PREEMPT_RT)) migrate_disable(); else preempt_disable(); pagefault_disable(); return page_address(page); } But kmap_local_page() is only having page_address(), the code block between kmap_local_page() and kunmap_local() is also atomic, it's a little messy in my mind. static inline void *kmap_local_page(struct page *page) { return page_address(page); } > + char *p = kaddr + offset; > + size_t copied = 0; > + > + if (!page_copy_sane(page, offset, bytes) || > + WARN_ON_ONCE(i->data_source)) > + goto out; > + > + if (unlikely(iov_iter_is_pipe(i))) { > + copied = copy_page_to_iter_pipe(page, offset, bytes, i); > + goto out; > + } > + > + iterate_and_advance(i, bytes, base, len, off, > + copyout(base, p + off, len), > + memcpy(base, p + off, len) > + ) > + copied = bytes; > + > +out: > + kunmap_local(kaddr); > + return copied; > +} > +EXPORT_SYMBOL(copy_page_to_iter_atomic); > + > static void pipe_advance(struct iov_iter *i, size_t size) > { > struct pipe_inode_info *pipe = i->pipe; > -- > 2.39.2 >