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Received: from willy by casper.infradead.org with local (Exim 4.94.2 #2 (Red Hat Linux)) id 1qKWOf-001nqR-9h; Sat, 15 Jul 2023 03:56:41 +0000 Date: Sat, 15 Jul 2023 04:56:41 +0100 From: Matthew Wilcox To: Miaohe Lin Cc: akpm@linux-foundation.org, hannes@cmpxchg.org, mhocko@kernel.org, roman.gushchin@linux.dev, shakeelb@google.com, muchun.song@linux.dev, linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm/memcg: use get_page() for device private pages in mc_handle_swap_pte() Message-ID: References: <20230715032802.2508163-1-linmiaohe@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230715032802.2508163-1-linmiaohe@huawei.com> X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: 81FA1A000D X-Stat-Signature: rb36hgpygnkt8eh489gpxp3qoc3oohe8 X-Rspam-User: X-HE-Tag: 1689393415-272196 X-HE-Meta: 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 JwM63JV7 y4jFl58gK3QzxmFPxsqeaejZD/rMXEi96E/22BUpt/jgHJiaWCxnSyGeppQi4libjLmqyUzr1VomlncgaqI9NHfBMI0L7oiVEiiaUk2mTC+JLuic0YOFlpGkmutkpQxnzFjatnUhjNEEykLlpldigxlg01pDvgwaia7eM/OFnkKMNQN6GWHTIrp0zPn/6aDl8MEI6/FWrdWlbLc0= 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 Sat, Jul 15, 2023 at 11:28:02AM +0800, Miaohe Lin wrote: > When page table locked is held, the page can't be freed from under us. But the page isn't mapped into the page table ... there's a swap entry in the page table, so I don't think your logic holds. > So use get_page() to get the extra page reference to simplify the code. > No functional change intended. > > Signed-off-by: Miaohe Lin > --- > mm/memcontrol.c | 5 +++-- > 1 file changed, 3 insertions(+), 2 deletions(-) > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index 93e3cc581b51..4ca382efb1ca 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -5670,8 +5670,9 @@ static struct page *mc_handle_swap_pte(struct vm_area_struct *vma, > */ > if (is_device_private_entry(ent)) { > page = pfn_swap_entry_to_page(ent); > - if (!get_page_unless_zero(page)) > - return NULL; > + /* Get a page reference while we know the page can't be freed. */ > + get_page(page); > + > return page; > } > > -- > 2.33.0 > >