From c42843f2f0bbc9d716a32caf667d18fc2bf3bc4c Mon Sep 17 00:00:00 2001 From: Wu Fengguang Date: Wed, 2 Mar 2011 15:54:09 -0600 Subject: writeback: introduce smoothed global dirty limit The start of a heavy weight application (ie. KVM) may instantly knock down determine_dirtyable_memory() if the swap is not enabled or full. global_dirty_limits() and bdi_dirty_limit() will in turn get global/bdi dirty thresholds that are _much_ lower than the global/bdi dirty pages. balance_dirty_pages() will then heavily throttle all dirtiers including the light ones, until the dirty pages drop below the new dirty thresholds. During this _deep_ dirty-exceeded state, the system may appear rather unresponsive to the users. About "deep" dirty-exceeded: task_dirty_limit() assigns 1/8 lower dirty threshold to heavy dirtiers than light ones, and the dirty pages will be throttled around the heavy dirtiers' dirty threshold and reasonably below the light dirtiers' dirty threshold. In this state, only the heavy dirtiers will be throttled and the dirty pages are carefully controlled to not exceed the light dirtiers' dirty threshold. However if the threshold itself suddenly drops below the number of dirty pages, the light dirtiers will get heavily throttled. So introduce global_dirty_limit for tracking the global dirty threshold with policies - follow downwards slowly - follow up in one shot global_dirty_limit can effectively mask out the impact of sudden drop of dirtyable memory. It will be used in the next patch for two new type of dirty limits. Note that the new dirty limits are not going to avoid throttling the light dirtiers, but could limit their sleep time to 200ms. Signed-off-by: Wu Fengguang --- include/linux/writeback.h | 6 ++++++ 1 file changed, 6 insertions(+) (limited to 'include') diff --git a/include/linux/writeback.h b/include/linux/writeback.h index 66862f2d90c8..e9d371b6053b 100644 --- a/include/linux/writeback.h +++ b/include/linux/writeback.h @@ -84,6 +84,8 @@ static inline void laptop_sync_completion(void) { } #endif void throttle_vm_writeout(gfp_t gfp_mask); +extern unsigned long global_dirty_limit; + /* These are exported to sysctl. */ extern int dirty_background_ratio; extern unsigned long dirty_background_bytes; @@ -119,6 +121,10 @@ unsigned long bdi_dirty_limit(struct backing_dev_info *bdi, unsigned long dirty); void __bdi_update_bandwidth(struct backing_dev_info *bdi, + unsigned long thresh, + unsigned long dirty, + unsigned long bdi_thresh, + unsigned long bdi_dirty, unsigned long start_time); void page_writeback_init(void); -- cgit v1.2.3