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Received: from willy by casper.infradead.org with local (Exim 4.98 #2 (Red Hat Linux)) id 1tJYkj-0000000EQ3S-0yQa; Fri, 06 Dec 2024 13:52:17 +0000 Date: Fri, 6 Dec 2024 13:52:16 +0000 From: Matthew Wilcox To: Jinjiang Tu Cc: Lorenzo Stoakes , Amir Goldstein , miklos@szeredi.hu, akpm@linux-foundation.org, vbabka@suse.cz, jannh@google.com, linux-mm@kvack.org, linux-unionfs@vger.kernel.org, wangkefeng.wang@huawei.com, sunnanyong@huawei.com, yi.zhang@huawei.com, Liam Howlett Subject: Re: [PATCH -next] ovl: respect underlying filesystem's get_unmapped_area() Message-ID: References: <20241205143038.3260233-1-tujinjiang@huawei.com> <69b72e3d-b101-4641-9ce5-51346c93a98d@lucifer.local> <518c881b-8ba0-df0e-16bf-00694c59f5a7@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <518c881b-8ba0-df0e-16bf-00694c59f5a7@huawei.com> X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: C7313C0007 X-Stat-Signature: r68pfi4m1n8c1atgfzsfxt3zu3xro9i7 X-Rspam-User: X-HE-Tag: 1733493125-282145 X-HE-Meta: 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 Q32ZbbRx PS0k1qHdhjBN7FcndEbXooHXLN8zw887CVDjnet3xfBB7C5e+x9Hk0AZ/FVoDT5li8Aulkvtdutf5/+4ac/zgFmpXloKMGJKxTmm+GTfuLtbl6FiYJ854ePNH4nBpywNtz+ixVbzxsBleJmotUra6awurE9C1yem+UNoBtqRZwlvHRKpDvo//ZLYEkW8GOml3TUmen7wIPDE0AOhhRfoZSGVMzB9oGSTVGNhz0w2HzhW9oGMIC+BcfBEPfLLSGTIkclgkfjNoJoF1lJFuKV0DY/MyaO2uNuXls2nK1nelB89O3aY= 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 Fri, Dec 06, 2024 at 11:35:20AM +0800, Jinjiang Tu wrote: > When usespace calls mmap syscall, the call trace is as follows: > > do_mmap >   __get_unmapped_area >   mmap_region >     mmap_file >       ovl_mmap > > __get_unmapped_area() gets the address to mmap at, the file here is an overlayfs file. > Since ovl_file_operations doesn't defines get_unmapped_area callback, __get_unmapped_area() > fallbacks to mm_get_unmapped_area_vmflags(), and it doesn't return an address aligned to > large folio size. It doesn't need to. large folios can be mapped at any alignment. The get_unmapped_area overrides are just for efficiency (ie be able to use PMD mappings when we happen to get a PMD-sized folio).