aboutsummaryrefslogtreecommitdiffstats
path: root/Documentation/filesystems/proc.txt
diff options
context:
space:
mode:
authorDavid Rientjes <rientjes@google.com>2009-01-06 17:39:31 -0500
committerLinus Torvalds <torvalds@linux-foundation.org>2009-01-06 18:59:03 -0500
commit2da02997e08d3efe8174c7a47696e6f7cbe69ba9 (patch)
tree2e52d9346c52dda83dc8cc9626cbe302e026ad9a /Documentation/filesystems/proc.txt
parent364aeb2849789b51bf4b9af2ddd02fee7285c54e (diff)
mm: add dirty_background_bytes and dirty_bytes sysctls
This change introduces two new sysctls to /proc/sys/vm: dirty_background_bytes and dirty_bytes. dirty_background_bytes is the counterpart to dirty_background_ratio and dirty_bytes is the counterpart to dirty_ratio. With growing memory capacities of individual machines, it's no longer sufficient to specify dirty thresholds as a percentage of the amount of dirtyable memory over the entire system. dirty_background_bytes and dirty_bytes specify quantities of memory, in bytes, that represent the dirty limits for the entire system. If either of these values is set, its value represents the amount of dirty memory that is needed to commence either background or direct writeback. When a `bytes' or `ratio' file is written, its counterpart becomes a function of the written value. For example, if dirty_bytes is written to be 8096, 8K of memory is required to commence direct writeback. dirty_ratio is then functionally equivalent to 8K / the amount of dirtyable memory: dirtyable_memory = free pages + mapped pages + file cache dirty_background_bytes = dirty_background_ratio * dirtyable_memory -or- dirty_background_ratio = dirty_background_bytes / dirtyable_memory AND dirty_bytes = dirty_ratio * dirtyable_memory -or- dirty_ratio = dirty_bytes / dirtyable_memory Only one of dirty_background_bytes and dirty_background_ratio may be specified at a time, and only one of dirty_bytes and dirty_ratio may be specified. When one sysctl is written, the other appears as 0 when read. The `bytes' files operate on a page size granularity since dirty limits are compared with ZVC values, which are in page units. Prior to this change, the minimum dirty_ratio was 5 as implemented by get_dirty_limits() although /proc/sys/vm/dirty_ratio would show any user written value between 0 and 100. This restriction is maintained, but dirty_bytes has a lower limit of only one page. Also prior to this change, the dirty_background_ratio could not equal or exceed dirty_ratio. This restriction is maintained in addition to restricting dirty_background_bytes. If either background threshold equals or exceeds that of the dirty threshold, it is implicitly set to half the dirty threshold. Acked-by: Peter Zijlstra <peterz@infradead.org> Cc: Dave Chinner <david@fromorbit.com> Cc: Christoph Lameter <cl@linux-foundation.org> Signed-off-by: David Rientjes <rientjes@google.com> Cc: Andrea Righi <righi.andrea@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'Documentation/filesystems/proc.txt')
-rw-r--r--Documentation/filesystems/proc.txt26
1 files changed, 25 insertions, 1 deletions
diff --git a/Documentation/filesystems/proc.txt b/Documentation/filesystems/proc.txt
index 71df353e367c..32e94635484f 100644
--- a/Documentation/filesystems/proc.txt
+++ b/Documentation/filesystems/proc.txt
@@ -1385,6 +1385,15 @@ swapcache reclaim. Decreasing vfs_cache_pressure causes the kernel to prefer
1385to retain dentry and inode caches. Increasing vfs_cache_pressure beyond 100 1385to retain dentry and inode caches. Increasing vfs_cache_pressure beyond 100
1386causes the kernel to prefer to reclaim dentries and inodes. 1386causes the kernel to prefer to reclaim dentries and inodes.
1387 1387
1388dirty_background_bytes
1389----------------------
1390
1391Contains the amount of dirty memory at which the pdflush background writeback
1392daemon will start writeback.
1393
1394If dirty_background_bytes is written, dirty_background_ratio becomes a function
1395of its value (dirty_background_bytes / the amount of dirtyable system memory).
1396
1388dirty_background_ratio 1397dirty_background_ratio
1389---------------------- 1398----------------------
1390 1399
@@ -1393,14 +1402,29 @@ pages + file cache, not including locked pages and HugePages), the number of
1393pages at which the pdflush background writeback daemon will start writing out 1402pages at which the pdflush background writeback daemon will start writing out
1394dirty data. 1403dirty data.
1395 1404
1405If dirty_background_ratio is written, dirty_background_bytes becomes a function
1406of its value (dirty_background_ratio * the amount of dirtyable system memory).
1407
1408dirty_bytes
1409-----------
1410
1411Contains the amount of dirty memory at which a process generating disk writes
1412will itself start writeback.
1413
1414If dirty_bytes is written, dirty_ratio becomes a function of its value
1415(dirty_bytes / the amount of dirtyable system memory).
1416
1396dirty_ratio 1417dirty_ratio
1397----------------- 1418-----------
1398 1419
1399Contains, as a percentage of the dirtyable system memory (free pages + mapped 1420Contains, as a percentage of the dirtyable system memory (free pages + mapped
1400pages + file cache, not including locked pages and HugePages), the number of 1421pages + file cache, not including locked pages and HugePages), the number of
1401pages at which a process which is generating disk writes will itself start 1422pages at which a process which is generating disk writes will itself start
1402writing out dirty data. 1423writing out dirty data.
1403 1424
1425If dirty_ratio is written, dirty_bytes becomes a function of its value
1426(dirty_ratio * the amount of dirtyable system memory).
1427
1404dirty_writeback_centisecs 1428dirty_writeback_centisecs
1405------------------------- 1429-------------------------
1406 1430