From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Maxim V. Patlasov" Subject: Re: [fuse-devel] [PATCH 14/14] mm: Account for WRITEBACK_TEMP in balance_dirty_pages Date: Thu, 25 Apr 2013 20:16:45 +0400 Message-ID: <517956ED.7060102@parallels.com> References: <20130401103749.19027.89833.stgit@maximpc.sw.ru> <20130401104250.19027.27795.stgit@maximpc.sw.ru> <51793DE6.3000503@parallels.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: Kirill Korotaev , Pavel Emelianov , "fuse-devel@lists.sourceforge.net" , Kernel Mailing List , James Bottomley , Al Viro , Linux-Fsdevel , , Andrew Morton , , To: Miklos Szeredi Return-path: In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-fsdevel.vger.kernel.org Hi, 04/25/2013 07:49 PM, Miklos Szeredi =D0=BF=D0=B8=D1=88=D0=B5=D1=82: > On Thu, Apr 25, 2013 at 4:29 PM, Maxim V. Patlasov > wrote: >>> diff --git a/mm/page-writeback.c b/mm/page-writeback.c >>> index 0713bfb..c47bcd4 100644 >>> --- a/mm/page-writeback.c >>> +++ b/mm/page-writeback.c >>> @@ -1235,7 +1235,8 @@ static void balance_dirty_pages(struct addres= s_space >>> *mapping, >>> */ >>> nr_reclaimable =3D global_page_state(NR_FILE_DIRTY= ) + >>> >>> global_page_state(NR_UNSTABLE_NFS); >>> - nr_dirty =3D nr_reclaimable + >>> global_page_state(NR_WRITEBACK); >>> + nr_dirty =3D nr_reclaimable + >>> global_page_state(NR_WRITEBACK) + >>> + global_page_state(NR_WRITEBACK_TEMP); >>> global_dirty_limits(&background_thresh, &dirty_thr= esh); >> >> Please drop this patch. As we discussed in LSF/MM, the fix above is = correct, >> but it's not enough: we also need to ensure disregard of NR_WRITEBAC= K_TEMP >> when balance_dirty_pages() is called from fuse daemon. I'll send a s= eparate >> patch-set soon. > Please elaborate. From a technical perspective "fuse daemon" is very > hard to define, so anything that relies on whether something came fro= m > the fuse daemon or not is conceptually broken. As Mel Gorman pointed out, fuse daemon diving into balance_dirty_pages=20 should not kick flusher judging on NR_WRITEBACK_TEMP. Essentially, all=20 we need in balance_dirty_pages is: if (I'm not fuse daemon) nr_dirty +=3D global_page_state(NR_WRITEBACK_TEMP); The way how to identify fuse daemon was not thoroughly scrutinized=20 during LSF/MM. Firstly, I thought it would be enough to set a=20 per-process flag handling fuse device open. But now I understand that=20 fuse daemon may be quite a complicated multi-threaded multi-process=20 construction. I'm going to add new FUSE_NOTIFY to allow fuse daemon=20 decide when it works on behalf of draining writeout-s. Having in mind=20 that fuse-lib is multi-threaded, I'm also going to inherit the flag on=20 copy_process(). Does it make sense for you? Also, another patch will put this ad-hoc FUSE_NOTIFY under fusermount=20 control. This will prevent malicious unprivileged fuse mounts from=20 setting the flag for malicious purposes. Thanks, Maxim