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McKenney" Cc: Andrew Morton , linux-mm , LKML , John Hubbard , John Dias Subject: Re: [PATCH] mm: fix is_pinnable_page against on cma page Message-ID: References: <20220502173558.2510641-1-minchan@kernel.org> <29d0c1c3-a44e-4573-7e7e-32be07544dbe@redhat.com> <08e9855c-395d-f40c-de3d-1ec8b644bfe8@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: BE884C0082 X-Stat-Signature: dyi1zyzhtq1mcb6sqypp5c749ap366af X-Rspam-User: Authentication-Results: imf10.hostedemail.com; dkim=pass header.d=gmail.com header.s=20210112 header.b="BvvJ/00V"; spf=pass (imf10.hostedemail.com: domain of minchan.kim@gmail.com designates 209.85.214.181 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-HE-Tag: 1651601553-410583 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 Tue, May 03, 2022 at 11:08:25AM -0700, Minchan Kim wrote: < snip > Ccing Paul really this time. Attach original code for Paul. diff --git a/include/linux/mm.h b/include/linux/mm.h index 6acca5cecbc5..f59bbe3296e3 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -1625,8 +1625,10 @@ static inline bool page_needs_cow_for_dma(struct vm_area_struct *vma, #ifdef CONFIG_MIGRATION static inline bool is_pinnable_page(struct page *page) { - return !(is_zone_movable_page(page) || is_migrate_cma_page(page)) || - is_zero_pfn(page_to_pfn(page)); + int mt = get_pageblock_migratetype(page); + + return !(is_zone_movable_page(page) || mt == MIGRATE_CMA || + mt == MIGRATE_ISOLATE || is_zero_pfn(page_to_pfn(page))); } #else static inline bool is_pinnable_page(struct page *page) -- 2.36.0.464.gb9c8b46e94-goog > > >>> > > >>> A thing to get some attention is whether we need READ_ONCE or not > > >>> for the local variable mt. > > >>> > > >> > > >> Hmm good point. Staring at __get_pfnblock_flags_mask(), I don't think > > >> there is anything stopping the compiler from re-reading the value. But > > >> we don't care if we're reading MIGRATE_CMA or MIGRATE_ISOLATE, not > > >> something in between. > > > > > > How about this? > > > > > > CPU A CPU B > > > > > > is_pinnable_page > > > .. > > > .. set_pageblock_migratetype(MIGRATE_ISOLATE) > > > mt == MIGRATE_CMA > > > get_pageblock_miratetype(page) > > > returns MIGRATE_ISOLATE > > > mt == MIGRATE_ISOLATE set_pageblock_migratetype(MIGRATE_CMA) > > > get_pageblock_miratetype(page) > > > returns MIGRATE_CMA > > > > > > So both conditions fails to detect it. > > > > I think you're right. That's nasty. > > Ccing Paul to borrow expertise. :) > > int mt = get_pageblock_migratetype(page); > > if (mt == MIGRATE_CMA) > return true; > > if (mt == MIGRATE_ISOLATE) > return true; > > I'd like to keep use the local variable mt's value in folloing > conditions checks instead of refetching the value from > get_pageblock_migratetype. > > What's the right way to achieve it? > > Thanks in advance! Paul, could you give any hint?