From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Mon, 22 Oct 2007 17:04:21 -0400 Message-Id: <200710222104.l9ML4L1D002031@agora.fsl.cs.sunysb.edu> From: Erez Zadok Subject: Re: msync(2) bug(?), returns AOP_WRITEPAGE_ACTIVATE to userland In-reply-to: Your message of "Mon, 22 Oct 2007 21:16:17 BST." Sender: owner-linux-mm@kvack.org Return-Path: To: Hugh Dickins Cc: Pekka Enberg , Erez Zadok , Ryan Finnie , Andrew Morton , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, cjwatson@ubuntu.com, linux-mm@kvack.org List-ID: In message , Hugh Dickins writes: > On Mon, 15 Oct 2007, Pekka Enberg wrote: > > > > I wonder whether _not setting_ BDI_CAP_NO_WRITEBACK implies that > > ->writepage() will never return AOP_WRITEPAGE_ACTIVATE for > > !wbc->for_reclaim case which would explain why we haven't hit this bug > > before. Hugh, Andrew? > > Only ramdisk and shmem have been returning AOP_WRITEPAGE_ACTIVATE. > Both of those set BDI_CAP_NO_WRITEBACK. ramdisk never returned it > if !wbc->for_reclaim. I contend that shmem shouldn't either: it's > a special code to get the LRU rotation right, not useful elsewhere. > Though Documentation/filesystems/vfs.txt does imply wider use. Yes, based on vfs.txt I figured unionfs should return AOP_WRITEPAGE_ACTIVATE. But, now that unionfs has ->writepages which won't even call the lower writepage if BDI_CAP_NO_WRITEBACK is on, then perhaps I no longer need unionfs_writepage to bother checking for AOP_WRITEPAGE_ACTIVATE, or even return it up? But, a future file system _could_ return AOP_WRITEPAGE_ACTIVATE w/o setting BDI_CAP_NO_WRITEBACK, right? In that case, unionfs will still need to handle AOP_WRITEPAGE_ACTIVATE in ->writepage, right? > I think this is where people use the phrase "go figure" ;) > > Hugh Erez. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org