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McKenney" , John Dias , David Hildenbrand Subject: Re: [PATCH v4] mm: fix is_pinnable_page against on cma page Message-ID: References: <2ffa7670-04ea-bb28-28f8-93a9b9eea7e8@nvidia.com> <54b5d177-f2f4-cef2-3a68-cd3b0b276f86@nvidia.com> <8f083802-7ab0-15ec-b37d-bc9471eea0b1@nvidia.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Stat-Signature: pfg9hhux8qt7nfrfe3ub6ujw9ytk1fk9 X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: C9406200A0 Authentication-Results: imf31.hostedemail.com; dkim=pass header.d=gmail.com header.s=20210112 header.b=brQstMvv; spf=pass (imf31.hostedemail.com: domain of minchan.kim@gmail.com designates 209.85.215.172 as permitted sender) smtp.mailfrom=minchan.kim@gmail.com; dmarc=fail reason="SPF not aligned (relaxed), DKIM not aligned (relaxed)" header.from=kernel.org (policy=none) X-Rspam-User: X-HE-Tag: 1652311662-739915 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 Wed, May 11, 2022 at 04:15:17PM -0700, Minchan Kim wrote: > On Wed, May 11, 2022 at 04:13:10PM -0700, John Hubbard wrote: > > On 5/11/22 16:08, Minchan Kim wrote: > > > > OK, so the code checks the wrong item each time. But the code really > > > > only needs to know "is either _CMA or _ISOLATE set?". And so you > > > > > > Yes. > > > > > > > can just sidestep the entire question by writing it like this: > > > > > > > > int mt = get_pageblock_migratetype(page); > > > > > > > > if (mt & (MIGRATE_ISOLATE | MIGRATE_CMA)) > > > > return false; > > > > > > I am confused. Isn't it same question? > > > > > > set_pageblock_migratetype(MIGRATE_ISOLATE) > > > if (get_pageblock_migrate(page) & MIGRATE_CMA) > > > > > > set_pageblock_migratetype(MIGRATE_CMA) > > > > > > if (get_pageblock_migrate(page) & MIGRATE_ISOLATE) > > > > Well no, because the "&" operation is a single operation on the CPU, and > > isn't going to get split up like that. > > Oh, if that's true, yeah, I could live with it. > > Thanks, let me post next revision with commenting about that. This is delta to confirm before posting next revision. Are you okay with this one? diff --git a/include/linux/mm.h b/include/linux/mm.h index cbf79eb790e0..7b2df6780552 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -1626,14 +1626,14 @@ static inline bool page_needs_cow_for_dma(struct vm_area_struct *vma, static inline bool is_pinnable_page(struct page *page) { #ifdef CONFIG_CMA + int mt = get_pageblock_migratetype(page); + /* - * use volatile to use local variable mt instead of - * refetching mt value. + * "&" operation would prevent compiler split up + * get_pageblock_migratetype two times for each + * condition check: refetching mt value two times. */ - int __mt = get_pageblock_migratetype(page); - int mt = __READ_ONCE(__mt); - - if (mt == MIGRATE_CMA || mt == MIGRATE_ISOLATE) + if (mt & (MIGRATE_ISOLATE | MIGRATE_CMA)) return false; #endif