Re: [PATCH] mm: strictlimit feature -v2

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



07/02/2013 11:38 PM, Andrew Morton пишет:
On Tue, 02 Jul 2013 21:44:47 +0400 Maxim Patlasov <MPatlasov@xxxxxxxxxxxxx> wrote:

From: Miklos Szeredi <mszeredi@xxxxxxx>

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:

Great! Thank you, Andrew. I'll wait for Fengguang' feedback for a while before respin.


...

@@ -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 from this list: send the line "unsubscribe linux-fsdevel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html




[Index of Archives]     [Linux Ext4 Filesystem]     [Union Filesystem]     [Filesystem Testing]     [Ceph Users]     [Ecryptfs]     [AutoFS]     [Kernel Newbies]     [Share Photos]     [Security]     [Netfilter]     [Bugtraq]     [Yosemite News]     [MIPS Linux]     [ARM Linux]     [Linux Security]     [Linux Cachefs]     [Reiser Filesystem]     [Linux RAID]     [Samba]     [Device Mapper]     [CEPH Development]
  Powered by Linux