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Subject[PATCH v6 8/9] 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() queries 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 v5:
- Simplified this change by using mem_cgroup_balance_dirty_pages() rather than
cramming the somewhat different logic into balance_dirty_pages(). This means
the global (non-memcg) dirty limits are not passed around in the
struct dirty_info, so there's less change to existing code.
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 | 34 ++++++++++++++++++++++++++++------
mm/vmscan.c | 2 +-
3 files changed, 31 insertions(+), 8 deletions(-)
diff --git a/include/linux/writeback.h b/include/linux/writeback.h
index 0ead399..a45d895 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;

@@ -92,7 +93,7 @@ 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 d8005b0..f6a8dd6 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -473,7 +473,8 @@ 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)
@@ -488,6 +489,8 @@ static void balance_dirty_pages(struct address_space *mapping,
bool dirty_exceeded = false;
struct backing_dev_info *bdi = mapping->backing_dev_info;

+ mem_cgroup_balance_dirty_pages(mapping, write_chunk);
+
for (;;) {
struct writeback_control wbc = {
.sync_mode = WB_SYNC_NONE,
@@ -651,23 +654,42 @@ 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. Both
+ * global dirty memory limits and (if @mem_cgroup is given) per-cgroup dirty
+ * memory limits are checked.
+ *
+ * If near limits, then wait for usage to drop. Dirty usage should drop because
+ * dirty producers should have used balance_dirty_pages(), which would have
+ * scheduled writeback.
+ */
+void throttle_vm_writeout(gfp_t gfp_mask, struct mem_cgroup *mem_cgroup)
{
unsigned long background_thresh;
unsigned long dirty_thresh;
+ struct dirty_info memcg_info;
+ bool do_memcg;

for ( ; ; ) {
global_dirty_limits(&background_thresh, &dirty_thresh);
+ do_memcg = mem_cgroup && mem_cgroup_hierarchical_dirty_info(
+ determine_dirtyable_memory(), true, mem_cgroup,
+ &memcg_info);

/*
* Boost the allowable dirty threshold a bit for page
* allocators so they don't get DoS'ed by heavy writers
*/
dirty_thresh += dirty_thresh / 10; /* wheeee... */
-
- if (global_page_state(NR_UNSTABLE_NFS) +
- global_page_state(NR_WRITEBACK) <= dirty_thresh)
- break;
+ if (do_memcg)
+ memcg_info.dirty_thresh += memcg_info.dirty_thresh / 10;
+
+ if ((global_page_state(NR_UNSTABLE_NFS) +
+ global_page_state(NR_WRITEBACK) <= dirty_thresh) &&
+ (!do_memcg ||
+ (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 060e4c1..035d2ea 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1939,7 +1939,7 @@ 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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