From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrew Morton Subject: Re: [PATCH] mm: strictlimit feature -v2 Date: Tue, 2 Jul 2013 12:38:04 -0700 Message-ID: <20130702123804.9f252487f86c12b0f4edee57@linux-foundation.org> References: <20130629174706.20175.78184.stgit@maximpc.sw.ru> <20130702174316.15075.84993.stgit@maximpc.sw.ru> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Cc: miklos@szeredi.hu, riel@redhat.com, dev@parallels.com, xemul@parallels.com, fuse-devel@lists.sourceforge.net, bfoster@redhat.com, linux-kernel@vger.kernel.org, jbottomley@parallels.com, linux-mm@kvack.org, viro@zeniv.linux.org.uk, linux-fsdevel@vger.kernel.org, fengguang.wu@intel.com, devel@openvz.org, mgorman@suse.de To: Maxim Patlasov Return-path: In-Reply-To: <20130702174316.15075.84993.stgit@maximpc.sw.ru> Sender: owner-linux-mm@kvack.org List-Id: linux-fsdevel.vger.kernel.org On Tue, 02 Jul 2013 21:44:47 +0400 Maxim Patlasov wrote: > From: Miklos Szeredi > > The feature prevents mistrusted filesystems to grow a large number of dirty > pages before throttling. For such filesystems balance_dirty_pages always > check bdi counters against bdi limits. I.e. even if global "nr_dirty" is under > "freerun", it's not allowed to skip bdi checks. The only use case for now is > fuse: it sets bdi max_ratio to 1% by default and system administrators are > supposed to expect that this limit won't be exceeded. > > The feature is on if address space is marked by AS_STRICTLIMIT flag. > A filesystem may set the flag when it initializes a new inode. > > Changed in v2 (thanks to Andrew Morton): > - added a few explanatory comments > - cleaned up the mess in backing_dev_info foo_stamp fields: now it's clearly > stated that bw_time_stamp is measured in jiffies; renamed other foo_stamp > fields to reflect that they are in units of number-of-pages. > Better, thanks. The writeback arithemtic makes my head spin - I'd really like Fengguang to go over this, please. A quick visit from the spelling police: > > ... > > @@ -41,8 +43,15 @@ typedef int (congested_fn)(void *, int); > enum bdi_stat_item { > BDI_RECLAIMABLE, > BDI_WRITEBACK, > - BDI_DIRTIED, > - BDI_WRITTEN, > + > + /* > + * The three counters below reflects number of events of specific type > + * happened since bdi_init(). The type is defined in comments below: "The three counters below reflect the number of events of specific types since bdi_init()" > + */ > + BDI_DIRTIED, /* a page was dirtied */ > + BDI_WRITTEN, /* writeout completed for a page */ > + BDI_WRITTEN_BACK, /* a page went to writeback */ > + > NR_BDI_STAT_ITEMS > }; > > > ... > > @@ -680,28 +712,55 @@ static unsigned long bdi_position_ratio(struct backing_dev_info *bdi, > return 0; > > /* > - * global setpoint > + * The strictlimit feature is a tool preventing mistrusted filesystems > + * to grow a large number of dirty pages before throttling. For such "from growing" > + * filesystems balance_dirty_pages always checks bdi counters against > + * bdi limits. Even if global "nr_dirty" is under "freerun". This is > + * especially important for fuse who sets bdi->max_ratio to 1% by s/who/which/ > + * default. Without strictlimit feature, fuse writeback may consume > + * arbitrary amount of RAM because it is accounted in > + * NR_WRITEBACK_TEMP which is not involved in calculating "nr_dirty". > > ... > > @@ -994,6 +1054,26 @@ static void bdi_update_dirty_ratelimit(struct backing_dev_info *bdi, > * keep that period small to reduce time lags). > */ > step = 0; > + > + /* > + * For strictlimit case, balanced_dirty_ratelimit was calculated balance_dirty_ratelimit? > + * above based on bdi counters and limits (see bdi_position_ratio()). > + * Hence, to calculate "step" properly, we have to use bdi_dirty as > + * "dirty" and bdi_setpoint as "setpoint". > + * > + * We rampup dirty_ratelimit forcibly if bdi_dirty is low because > + * it's possible that bdi_thresh is close to zero due to inactivity > + * of backing device (see the implementation of bdi_dirty_limit()). > + */ > + if (unlikely(strictlimit)) { > + dirty = bdi_dirty; > + if (bdi_dirty < 8) > + setpoint = bdi_dirty + 1; > + else > > ... > > @@ -1057,18 +1140,32 @@ void __bdi_update_bandwidth(struct backing_dev_info *bdi, > if (elapsed > HZ && time_before(bdi->bw_time_stamp, start_time)) > goto snapshot; > > + /* > + * Skip periods when backing dev was idle due to abscence of pages "absence" > + * under writeback (when over_bground_thresh() returns false) > + */ > + if (test_bit(BDI_idle, &bdi->state) && > + bdi->writeback_nr_stamp == writeback) > > ... > -- 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