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Shutemov" CC: Andrew Morton , Al Viro , Christoph Hellwig , Dan Williams , Dave Chinner , Ira Weiny , Jan Kara , Jason Gunthorpe , Jonathan Corbet , =?UTF-8?B?SsOpcsO0bWUgR2xpc3Nl?= , Michal Hocko , Mike Kravetz , Shuah Khan , Vlastimil Babka , Matthew Wilcox , , , , , , LKML References: <20200201034029.4063170-1-jhubbard@nvidia.com> <20200201034029.4063170-5-jhubbard@nvidia.com> <20200203132329.oj32h4ryna4gmkwh@box> X-Nvconfidentiality: public From: John Hubbard Message-ID: Date: Mon, 3 Feb 2020 12:03:49 -0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.4.2 MIME-Version: 1.0 In-Reply-To: <20200203132329.oj32h4ryna4gmkwh@box> X-Originating-IP: [10.124.1.5] X-ClientProxiedBy: HQMAIL105.nvidia.com (172.20.187.12) To HQMAIL107.nvidia.com (172.20.187.13) Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 7bit DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=nvidia.com; s=n1; t=1580760216; bh=slWoAOjCgnvUbCzYd3p0ud2KsXbx4UbZ3i/D9mUZD1g=; h=X-PGP-Universal:Subject:To:CC:References:X-Nvconfidentiality:From: Message-ID:Date:User-Agent:MIME-Version:In-Reply-To: X-Originating-IP:X-ClientProxiedBy:Content-Type:Content-Language: Content-Transfer-Encoding; b=oVZNVkNOYc+kjHjL1ubbfOHYXpU03ACYQb+0iGYED3N00qAA3rTqLUI6W/FLL+/94 /0KeKWTUWnMIexwZe5JmSqXp+kb8hJtQy0qeXMnTlnzW+b9F2iWiGnPnnt9cE9x8i/ 5STz78HwfzxwIVZPLujhbB4GRDXG5qsYqBngJ+h0QUog4ruNYP7jhqKRoTVJibYTtb a5Zzlj4qk7geaex9f3KLWk/NEEPuHZInTpHE7rcDuc1a+AITXTK3Kr/YvNFR/r+NMN W/eQjpACACV53Umd/t7HWidJT6UkHnNwf4WNStZTM+x7tku5YdYyA+1ka/W79nkeIP FYwSgB6uujrlg== 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 2/3/20 5:23 AM, Kirill A. Shutemov wrote: > On Fri, Jan 31, 2020 at 07:40:21PM -0800, John Hubbard wrote: >> An upcoming patch requires subtracting a large chunk of refcounts from >> a page, and checking what the resulting refcount is. This is a little >> different than the usual "check for zero refcount" that many of the >> page ref functions already do. However, it is similar to a few other >> routines that (like this one) are generally useful for things such as >> 1-based refcounting. >> >> Add page_ref_sub_return(), that subtracts a chunk of refcounts >> atomically, and returns an atomic snapshot of the result. >> >> Signed-off-by: John Hubbard >> --- >> include/linux/page_ref.h | 10 ++++++++++ >> 1 file changed, 10 insertions(+) >> >> diff --git a/include/linux/page_ref.h b/include/linux/page_ref.h >> index 14d14beb1f7f..b9cbe553d1e7 100644 >> --- a/include/linux/page_ref.h >> +++ b/include/linux/page_ref.h >> @@ -102,6 +102,16 @@ static inline void page_ref_sub(struct page *page, int nr) >> __page_ref_mod(page, -nr); >> } >> >> +static inline int page_ref_sub_return(struct page *page, int nr) >> +{ >> + int ret = atomic_sub_return(nr, &page->_refcount); >> + >> + if (page_ref_tracepoint_active(__tracepoint_page_ref_mod)) >> + __page_ref_mod(page, -nr); > > Shouldn't it be __page_ref_mod_and_return() and relevant tracepoint? Why yes, it should. I didn't even notice that that more precise function existed, thanks for catching that. I've changed it to this for the next version of the patchset: static inline int page_ref_sub_return(struct page *page, int nr) { int ret = atomic_sub_return(nr, &page->_refcount); if (page_ref_tracepoint_active(__tracepoint_page_ref_mod)) __page_ref_mod_and_return(page, -nr, ret); return ret; } thanks, -- John Hubbard NVIDIA > >> + >> + return ret; >> +} >> + >> static inline void page_ref_inc(struct page *page) >> { >> atomic_inc(&page->_refcount); >> -- >> 2.25.0 >> >