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Received: from willy by casper.infradead.org with local (Exim 4.98 #2 (Red Hat Linux)) id 1tW6gd-0000000BP7a-2d0i; Fri, 10 Jan 2025 04:31:55 +0000 Date: Fri, 10 Jan 2025 04:31:55 +0000 From: Matthew Wilcox To: Yang Shi Cc: Liu Shixin , Andrew Morton , Chengming Zhou , Kefeng Wang , Nanyong Sun , Muchun Song , Qi Zheng , Johannes Weiner , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm: khugepaged: fix call hpage_collapse_scan_file() for anonymous vma Message-ID: References: <20250109070059.369257-1-liushixin2@huawei.com> <037d4442-4d2d-4aeb-8091-5efffc374d36@os.amperecomputing.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <037d4442-4d2d-4aeb-8091-5efffc374d36@os.amperecomputing.com> X-Rspamd-Queue-Id: D244518000B X-Rspam-User: X-Rspamd-Server: rspam07 X-Stat-Signature: m8cjggtxid1fg4ghrez8py89x6unz35u X-HE-Tag: 1736483528-305872 X-HE-Meta: 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 MlFaP5bA ZVfQXUX2G5mCq+XZD/iU+RetYpIi34Ht+yW9MsMqs4LoFCecHQJiQ7tzt1OX8y9nCawdnJMY4F04fxooi6BktlUymNzlePawIodZ1HYubzzLeK8ps3Q03otQWbEvsQyL9jQpbQopwN0+XMtE6Vz1IpD4ZSOVrlm/TmqBoEbak3O9OZbuiqhbd1hp3NU2NwcuLsitBoABjdW4PcrsYKyrEPngMZ6j8+umeH7DoKsvzG/ElcYnDT8uQUeAntUR4+HqNT+V513OsC2eK3lHGBRKZa+4TEBmCKe/tgEZSZZ7PTuNvL5c= 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: List-Subscribe: List-Unsubscribe: On Thu, Jan 09, 2025 at 09:00:24AM -0800, Yang Shi wrote: > Thanks for catching this. It sounds a little bit weird to have vm_file for > an anonymous VMA. I'm not sure why we should keep such special case. It > seems shared mapping is treated as shmem file mapping. So can we set vm_file > to NULL when mmap'ing /dev/zero for private mapping? Something like: > > diff --git a/drivers/char/mem.c b/drivers/char/mem.c > index 169eed162a7f..fc332efc5c11 100644 > --- a/drivers/char/mem.c > +++ b/drivers/char/mem.c > @@ -527,6 +527,7 @@ static int mmap_zero(struct file *file, struct > vm_area_struct *vma) >         if (vma->vm_flags & VM_SHARED) >                 return shmem_zero_setup(vma); >         vma_set_anonymous(vma); > +       vma->vm_file = NULL; >         return 0; >  } I'm wary this might cause other bugs somewhere. rc6 is a bit late to be introducing such a subtle change.