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Subject[PATCH v5 9/9] memcg: check memcg dirty limits in page writeback
Date
If the current process is in a non-root memcg, then
balance_dirty_pages() will consider the memcg dirty limits as well as
the system-wide limits. This allows different cgroups to have distinct
dirty limits which trigger direct and background writeback at different
levels.

If called with a mem_cgroup, then throttle_vm_writeout() should query
the given cgroup for its dirty memory usage limits.

Signed-off-by: Andrea Righi <arighi@develer.com>
Signed-off-by: Greg Thelen <gthelen@google.com>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Acked-by: Wu Fengguang <fengguang.wu@intel.com>
---
Changelog since v4:
- Added missing 'struct mem_cgroup' forward declaration in writeback.h.
- Made throttle_vm_writeout() memcg aware.
- Removed previously added dirty_writeback_pages() which is no longer needed.
- Added logic to balance_dirty_pages() to throttle if over foreground memcg
limit.
Changelog since v3:
- Leave determine_dirtyable_memory() static. v3 made is non-static.
- balance_dirty_pages() now considers both system and memcg dirty limits and
usage data. This data is retrieved with global_dirty_info() and
memcg_dirty_info().

include/linux/writeback.h | 3 +-
mm/page-writeback.c | 112 +++++++++++++++++++++++++++++++++------------
mm/vmscan.c | 2 +-
3 files changed, 86 insertions(+), 31 deletions(-)
diff --git a/include/linux/writeback.h b/include/linux/writeback.h
index a06fb38..e4688d6 100644
--- a/include/linux/writeback.h
+++ b/include/linux/writeback.h
@@ -8,6 +8,7 @@
#include <linux/fs.h>

struct backing_dev_info;
+struct mem_cgroup;

extern spinlock_t inode_lock;

@@ -105,7 +106,7 @@ void laptop_mode_timer_fn(unsigned long data);
#else
static inline void laptop_sync_completion(void) { }
#endif
-void throttle_vm_writeout(gfp_t gfp_mask);
+void throttle_vm_writeout(gfp_t gfp_mask, struct mem_cgroup *mem_cgroup);

/* These are exported to sysctl. */
extern int dirty_background_ratio;
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 8d61cfa..5557e0c 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -398,47 +398,72 @@ unsigned long determine_dirtyable_memory(void)
}

/*
+ * The dirty limits will be lifted by 1/4 for PF_LESS_THROTTLE (ie. nfsd) and
+ * real-time tasks.
+ */
+static inline void adjust_dirty_info(struct dirty_info *info)
+{
+ struct task_struct *tsk;
+
+ if (info->background_thresh >= info->dirty_thresh)
+ info->background_thresh = info->dirty_thresh / 2;
+ tsk = current;
+ if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk)) {
+ info->background_thresh += info->background_thresh / 4;
+ info->dirty_thresh += info->dirty_thresh / 4;
+ }
+}
+
+/*
* global_dirty_info - return dirty thresholds and usage metrics
*
* Calculate the dirty thresholds based on sysctl parameters
* - vm.dirty_background_ratio or vm.dirty_background_bytes
* - vm.dirty_ratio or vm.dirty_bytes
- * The dirty limits will be lifted by 1/4 for PF_LESS_THROTTLE (ie. nfsd) and
- * real-time tasks.
*/
void global_dirty_info(struct dirty_info *info)
{
- unsigned long background;
- unsigned long dirty;
unsigned long uninitialized_var(available_memory);
- struct task_struct *tsk;

if (!vm_dirty_bytes || !dirty_background_bytes)
available_memory = determine_dirtyable_memory();

if (vm_dirty_bytes)
- dirty = DIV_ROUND_UP(vm_dirty_bytes, PAGE_SIZE);
+ info->dirty_thresh = DIV_ROUND_UP(vm_dirty_bytes, PAGE_SIZE);
else
- dirty = (vm_dirty_ratio * available_memory) / 100;
+ info->dirty_thresh = (vm_dirty_ratio * available_memory) / 100;

if (dirty_background_bytes)
- background = DIV_ROUND_UP(dirty_background_bytes, PAGE_SIZE);
+ info->background_thresh =
+ DIV_ROUND_UP(dirty_background_bytes, PAGE_SIZE);
else
- background = (dirty_background_ratio * available_memory) / 100;
+ info->background_thresh =
+ (dirty_background_ratio * available_memory) / 100;

info->nr_file_dirty = global_page_state(NR_FILE_DIRTY);
info->nr_writeback = global_page_state(NR_WRITEBACK);
info->nr_unstable_nfs = global_page_state(NR_UNSTABLE_NFS);

- if (background >= dirty)
- background = dirty / 2;
- tsk = current;
- if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk)) {
- background += background / 4;
- dirty += dirty / 4;
- }
- info->background_thresh = background;
- info->dirty_thresh = dirty;
+ adjust_dirty_info(info);
+}
+
+/*
+ * Calculate the background-writeback and dirty-throttling thresholds and dirty
+ * usage metrics from the current task's memcg dirty limit parameters. Returns
+ * false if no memcg limits exist.
+ *
+ * @memcg may be NULL if the current task's memcg should be used.
+ * @info is the location where the dirty information is written.
+ */
+static bool memcg_dirty_info(struct mem_cgroup *memcg, struct dirty_info *info)
+{
+ unsigned long available_memory = determine_dirtyable_memory();
+
+ if (!mem_cgroup_hierarchical_dirty_info(available_memory, memcg, info))
+ return false;
+
+ adjust_dirty_info(info);
+ return true;
}

/*
@@ -477,12 +502,14 @@ unsigned long bdi_dirty_limit(struct backing_dev_info *bdi, unsigned long dirty)
* data. It looks at the number of dirty pages in the machine and will force
* the caller to perform writeback if the system is over `vm_dirty_ratio'.
* If we're over `background_thresh' then the writeback threads are woken to
- * perform some writeout.
+ * perform some writeout. The current task may have per-memcg dirty
+ * limits, which are also checked.
*/
static void balance_dirty_pages(struct address_space *mapping,
unsigned long write_chunk)
{
struct dirty_info sys_info;
+ struct dirty_info memcg_info;
long bdi_nr_reclaimable;
long bdi_nr_writeback;
unsigned long bdi_thresh;
@@ -500,18 +527,27 @@ static void balance_dirty_pages(struct address_space *mapping,
};

global_dirty_info(&sys_info);
+ if (!memcg_dirty_info(NULL, &memcg_info))
+ memcg_info = sys_info;

/*
* Throttle it only when the background writeback cannot
* catch-up. This avoids (excessively) small writeouts
* when the bdi limits are ramping up.
*/
- if (dirty_info_reclaimable(&sys_info) + sys_info.nr_writeback <=
+ if ((dirty_info_reclaimable(&sys_info) +
+ sys_info.nr_writeback <=
(sys_info.background_thresh +
- sys_info.dirty_thresh) / 2)
+ sys_info.dirty_thresh) / 2) &&
+ (dirty_info_reclaimable(&memcg_info) +
+ memcg_info.nr_writeback <=
+ (memcg_info.background_thresh +
+ memcg_info.dirty_thresh) / 2))
break;

- bdi_thresh = bdi_dirty_limit(bdi, sys_info.dirty_thresh);
+ bdi_thresh = bdi_dirty_limit(bdi,
+ min(sys_info.dirty_thresh,
+ memcg_info.dirty_thresh));
bdi_thresh = task_dirty_limit(current, bdi_thresh);

/*
@@ -541,7 +577,9 @@ static void balance_dirty_pages(struct address_space *mapping,
dirty_exceeded =
(bdi_nr_reclaimable + bdi_nr_writeback > bdi_thresh)
|| (dirty_info_reclaimable(&sys_info) +
- sys_info.nr_writeback > sys_info.dirty_thresh);
+ sys_info.nr_writeback > sys_info.dirty_thresh)
+ || (dirty_info_reclaimable(&memcg_info) +
+ memcg_info.nr_writeback > memcg_info.dirty_thresh);

if (!dirty_exceeded)
break;
@@ -559,7 +597,9 @@ static void balance_dirty_pages(struct address_space *mapping,
* up.
*/
trace_wbc_balance_dirty_start(&wbc, bdi);
- if (bdi_nr_reclaimable > bdi_thresh) {
+ if ((bdi_nr_reclaimable > bdi_thresh) ||
+ (dirty_info_reclaimable(&memcg_info) >
+ memcg_info.dirty_thresh)) {
writeback_inodes_wb(&bdi->wb, &wbc);
pages_written += write_chunk - wbc.nr_to_write;
trace_wbc_balance_dirty_written(&wbc, bdi);
@@ -594,8 +634,10 @@ static void balance_dirty_pages(struct address_space *mapping,
* background_thresh, to keep the amount of dirty memory low.
*/
if ((laptop_mode && pages_written) ||
- (!laptop_mode && (dirty_info_reclaimable(&sys_info) >
- sys_info.background_thresh)))
+ (!laptop_mode && ((dirty_info_reclaimable(&sys_info) >
+ sys_info.background_thresh) ||
+ (dirty_info_reclaimable(&memcg_info) >
+ memcg_info.background_thresh))))
bdi_start_background_writeback(bdi);
}

@@ -653,12 +695,20 @@ void balance_dirty_pages_ratelimited_nr(struct address_space *mapping,
}
EXPORT_SYMBOL(balance_dirty_pages_ratelimited_nr);

-void throttle_vm_writeout(gfp_t gfp_mask)
+/*
+ * Throttle the current task if it is near dirty memory usage limits.
+ * If @mem_cgroup is NULL or the root_cgroup, then use global dirty memory
+ * information; otherwise use the per-memcg dirty limits.
+ */
+void throttle_vm_writeout(gfp_t gfp_mask, struct mem_cgroup *mem_cgroup)
{
struct dirty_info sys_info;
+ struct dirty_info memcg_info;

for ( ; ; ) {
global_dirty_info(&sys_info);
+ if (!memcg_dirty_info(mem_cgroup, &memcg_info))
+ memcg_info = sys_info;

/*
* Boost the allowable dirty threshold a bit for page
@@ -666,9 +716,13 @@ void throttle_vm_writeout(gfp_t gfp_mask)
*/
sys_info.dirty_thresh +=
sys_info.dirty_thresh / 10; /* wheeee... */
+ memcg_info.dirty_thresh +=
+ memcg_info.dirty_thresh / 10; /* wheeee... */

- if (sys_info.nr_unstable_nfs +
- sys_info.nr_writeback <= sys_info.dirty_thresh)
+ if ((sys_info.nr_unstable_nfs +
+ sys_info.nr_writeback <= sys_info.dirty_thresh) &&
+ (memcg_info.nr_unstable_nfs +
+ memcg_info.nr_writeback <= memcg_info.dirty_thresh))
break;
congestion_wait(BLK_RW_ASYNC, HZ/10);

diff --git a/mm/vmscan.c b/mm/vmscan.c
index ba11e28..f723242 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1927,7 +1927,7 @@ restart:
sc->nr_scanned - nr_scanned, sc))
goto restart;

- throttle_vm_writeout(sc->gfp_mask);
+ throttle_vm_writeout(sc->gfp_mask, sc->mem_cgroup);
}

/*
--
1.7.3.1


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