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Thu, 19 Aug 2021 23:34:02 -0700 (PDT) MIME-Version: 1.0 References: <20210813063150.2938-1-alex.sierra@amd.com> <20210813063150.2938-3-alex.sierra@amd.com> <20210815153713.GA32384@lst.de> <387d5f85-3d15-9a9e-2382-6ce3c14bc6d5@nvidia.com> In-Reply-To: <387d5f85-3d15-9a9e-2382-6ce3c14bc6d5@nvidia.com> From: Jerome Glisse Date: Thu, 19 Aug 2021 23:33:50 -0700 Message-ID: Subject: Re: [PATCH v6 02/13] mm: remove extra ZONE_DEVICE struct page refcount To: John Hubbard Cc: Christoph Hellwig , Alex Sierra , Andrew Morton , "Kuehling, Felix" , linux-mm@kvack.org, Ralph Campbell , linux-ext4@vger.kernel.org, linux-xfs@vger.kernel.org, amd-gfx list , Maling list - DRI developers , jgg@nvidia.com, Jerome Glisse Content-Type: text/plain; charset="UTF-8" X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: 97CA220019CF X-Stat-Signature: uqpd94o4qktp9afjah9itjkpjxznxkb9 Authentication-Results: imf26.hostedemail.com; dkim=pass header.d=gmail.com header.s=20161025 header.b=X3lZPbwo; dmarc=pass (policy=none) header.from=gmail.com; spf=pass (imf26.hostedemail.com: domain of jglisse@gmail.com designates 209.85.218.49 as permitted sender) smtp.mailfrom=jglisse@gmail.com X-HE-Tag: 1629441243-284997 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: Note that you do not want GUP to succeed on device page, i do not see where that is handled in the new code. On Sun, Aug 15, 2021 at 1:40 PM John Hubbard wrote: > > On 8/15/21 8:37 AM, Christoph Hellwig wrote: > >> diff --git a/include/linux/mm.h b/include/linux/mm.h > >> index 8ae31622deef..d48a1f0889d1 100644 > >> --- a/include/linux/mm.h > >> +++ b/include/linux/mm.h > >> @@ -1218,7 +1218,7 @@ __maybe_unused struct page *try_grab_compound_head(struct page *page, int refs, > >> static inline __must_check bool try_get_page(struct page *page) > >> { > >> page = compound_head(page); > >> - if (WARN_ON_ONCE(page_ref_count(page) <= 0)) > >> + if (WARN_ON_ONCE(page_ref_count(page) < (int)!is_zone_device_page(page))) > > > > Please avoid the overly long line. In fact I'd be tempted to just not > > bother here and keep the old, more lose check. Especially given that > > John has a patch ready that removes try_get_page entirely. > > > > Yes. Andrew has accepted it into mmotm. > > Ralph's patch here was written well before my cleanup that removed > try_grab_page() [1]. But now that we're here, if you drop this hunk then > it will make merging easier, I think. > > > [1] https://lore.kernel.org/r/20210813044133.1536842-4-jhubbard@nvidia.com > > thanks, > -- > John Hubbard > NVIDIA >