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Received: from willy by casper.infradead.org with local (Exim 4.98.2 #2 (Red Hat Linux)) id 1uMCyu-00000001MIc-0oeF; Mon, 02 Jun 2025 21:46:08 +0000 Date: Mon, 2 Jun 2025 22:46:08 +0100 From: Matthew Wilcox To: Steven Rostedt Cc: LKML , linux-mm@kvack.org, Hugh Dickins , Andrew Morton , Linus Torvalds Subject: Re: [PATCH] mm: Fix compile error when CONFIG_SHMEM is not set Message-ID: References: <20250602170500.48713a2b@gandalf.local.home> <20250602171458.7ceabb1c@gandalf.local.home> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250602171458.7ceabb1c@gandalf.local.home> X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 04C3018000A X-Stat-Signature: ku3roctt9b7f1xhwybncr3tj3tim13cb X-Rspam-User: X-HE-Tag: 1748900770-336942 X-HE-Meta: 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 TXlMDkAG tGZxwcH9w4KNgyMT73bergreH2HoA5KcmkFL+l+AVxUVvoaftTNxatyVsIsn5KRrcBTjWm714U2LkF3YI6xu65wughbcNe9ec1Yp53tmQ/HZG9iebmX7Rb9CpdPVBvYHJHeyhsH8LYsurlqYgy7aXkooWsc9O0piXElM+dNgemhizoh3cgogNYIGFGt1WqR5RoyOjBUI2ObK246U1hZ0ZF/VUL9DOVyaJMa4+Zsb39QjmUDJMEOGbV8oWl07KrEq0Cw9RkbePoVHJw3FJNO93OHkNol/Yie2wQ3vyNDu2HdAqI+Ss8xE2SHc0e+cfNMpm4033mJsJqtK0Xu8= 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 Mon, Jun 02, 2025 at 05:14:58PM -0400, Steven Rostedt wrote: > On Mon, 2 Jun 2025 17:05:00 -0400 > Steven Rostedt wrote: > > > From: Steven Rostedt > > > > When CONFIG_SHMEM is not set, the following compiler error occurs: > > > > ld: vmlinux.o: in function `ttm_backup_backup_page': > > I'm not sure this is the right fix or not. > > +int shmem_writeout(struct folio *folio, struct writeback_control *wbc) > > +{ > > + return 0; > > Perhaps this should return: > > return swap_writeout(folio, wbc); I don't think so. ttm_backup_backup_page() gets its page from: to_folio = shmem_read_folio_gfp(mapping, idx, alloc_gfp); ... ret = shmem_writeout(to_folio, &wbc); and if you look at the implementation of shmem_read_folio_gfp() does: #else /* * The tiny !SHMEM case uses ramfs without swap */ return mapping_read_folio_gfp(mapping, index, gfp); #endif so I would say that if anybody is actually using it this way (and 99% chance they're not), they literally cannot write back the folio. So I think your initial patch is fine.