On Sat, 29 Jun 2013 21:48:54 +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.
Fengguang, could you please review this patch?
I suggest you await the next version, which hopefully will be more
reviewable...
BDI_unused, /* Available bits start here */
};
@@ -43,6 +45,7 @@ enum bdi_stat_item {
BDI_WRITEBACK,
BDI_DIRTIED,
BDI_WRITTEN,
+ BDI_WRITTEN_BACK,
NR_BDI_STAT_ITEMS
};
@@ -76,6 +79,8 @@ struct backing_dev_info {
unsigned long bw_time_stamp; /* last time write bw is updated */
unsigned long dirtied_stamp;
unsigned long written_stamp; /* pages written at bw_time_stamp */
+ unsigned long writeback_stamp; /* pages sent to writeback at
+ * bw_time_stamp */
Well this sucks. Some of the "foo_stamp" fields are in units of time
(jiffies? We aren't told) and some of the "foo_stamp" fields are in
units of number-of-pages. It would be good to fix the naming here.
unsigned long write_bandwidth; /* the estimated write bandwidth */
unsigned long avg_write_bandwidth; /* further smoothed write bw */
diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index e3dea75..baac702 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -25,6 +25,7 @@ enum mapping_flags {
AS_MM_ALL_LOCKS = __GFP_BITS_SHIFT + 2, /* under mm_take_all_locks() */
AS_UNEVICTABLE = __GFP_BITS_SHIFT + 3, /* e.g., ramdisk, SHM_LOCK */
AS_BALLOON_MAP = __GFP_BITS_SHIFT + 4, /* balloon page special map */
+ AS_STRICTLIMIT = __GFP_BITS_SHIFT + 5, /* strict dirty limit */
Thing is, "strict dirty limit" isn't documented anywhere, so this
reference is left dangling.
...
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -94,6 +94,7 @@ static int bdi_debug_stats_show(struct seq_file *m, void *v)
"BackgroundThresh: %10lu kB\n"
"BdiDirtied: %10lu kB\n"
"BdiWritten: %10lu kB\n"
+ "BdiWrittenBack: %10lu kB\n"
"BdiWriteBandwidth: %10lu kBps\n"
"b_dirty: %10lu\n"
"b_io: %10lu\n"
I can't imagine what the difference is between BdiWritten and
BdiWrittenBack.
I suggest you document this at the BDI_WRITTEN_BACK definition site in
enum bdi_stat_item. BDI_WRITTEN (at least) will also need
documentation so people can understand the difference.
...
@@ -679,29 +711,31 @@ static unsigned long bdi_position_ratio(struct backing_dev_info *bdi,
if (unlikely(dirty >= limit))
return 0;
+ if (unlikely(strictlimit)) {
+ if (bdi_dirty < 8)
+ return 2 << RATELIMIT_CALC_SHIFT;
+
+ if (bdi_dirty >= bdi_thresh)
+ return 0;
+
+ bdi_setpoint = bdi_thresh + bdi_dirty_limit(bdi, bg_thresh);
+ bdi_setpoint /= 2;
+
+ if (bdi_setpoint == 0 || bdi_setpoint == bdi_thresh)
+ return 0;
+
+ pos_ratio = pos_ratio_polynom(bdi_setpoint, bdi_dirty,
+ bdi_thresh);
+ return min_t(long long, pos_ratio, 2 << RATELIMIT_CALC_SHIFT);
+ }
This would be a suitable site at which to document the strictlimit
feature. What it is, how it works and most importantly, why it exists.
...
@@ -994,6 +1029,16 @@ static void bdi_update_dirty_ratelimit(struct backing_dev_info *bdi,
* keep that period small to reduce time lags).
*/
step = 0;
+
+ if (unlikely(strictlimit)) {
+ dirty = bdi_dirty;
+ if (bdi_dirty < 8)
+ setpoint = bdi_dirty + 1;
+ else
+ setpoint = (bdi_thresh +
+ bdi_dirty_limit(bdi, bg_thresh)) / 2;
+ }
Explain this to the reader, please.
...
