[PATCH v3 0/2] mm: memcontrol: memory.{low,min} reclaim fix & cleanup

[PATCH v3 0/2] mm: memcontrol: memory.{low,min} reclaim fix & cleanup

[Yafang Shao]

This series contains a fix for a edge case in my earlier protection
calculation patches, and a patch to make the area overall a little more
robust to hopefully help avoid this in future.

[chris@chrisdown.name: commit log above]

Changes since v2: commit log improved by Michal.

Chris Down (1):
  mm, memcg: Decouple e{low,min} state mutations from protection checks

Yafang Shao (1):
  mm, memcg: Avoid stale protection values when cgroup is above
    protection

 include/linux/memcontrol.h | 85 ++++++++++++++++++++++++++++++++------
 mm/memcontrol.c            | 36 +++++++---------
 mm/vmscan.c                | 20 +++------
 3 files changed, 93 insertions(+), 48 deletions(-)

-- 
2.18.2

[PATCH v3 1/2] mm, memcg: Avoid stale protection values when cgroup is above protection

[Yafang Shao]

A cgroup can have both memory protection and a memory limit to isolate
it from its siblings in both directions - for example, to prevent it
from being shrunk below 2G under high pressure from outside, but also
from growing beyond 4G under low pressure.

Commit 9783aa9917f8 ("mm, memcg: proportional memory.{low,min} reclaim")
implemented proportional scan pressure so that multiple siblings in
excess of their protection settings don't get reclaimed equally but
instead in accordance to their unprotected portion.

During limit reclaim, this proportionality shouldn't apply of course:
there is no competition, all pressure is from within the cgroup and
should be applied as such. Reclaim should operate at full efficiency.

However, mem_cgroup_protected() never expected anybody to look at the
effective protection values when it indicated that the cgroup is above
its protection. As a result, a query during limit reclaim may return
stale protection values that were calculated by a previous reclaim cycle
in which the cgroup did have siblings.

When this happens, reclaim is unnecessarily hesitant and potentially
slow to meet the desired limit. In theory this could lead to premature
OOM kills, although it's not obvious this has occurred in practice.

Workaround the problem by special casing reclaim roots in
mem_cgroup_protection. These memcgs are never participating in the
reclaim protection because the reclaim is internal.

We have to ignore effective protection values for reclaim roots because
mem_cgroup_protected might be called from racing reclaim contexts with
different roots. Calculation is relying on root -> leaf tree traversal
therefore top-down reclaim protection invariants should hold. The only
exception is the reclaim root which should have effective protection set
to 0 but that would be problematic for the following setup:
 Let's have global and A's reclaim in parallel:
  |
  A (low=2G, usage = 3G, max = 3G, children_low_usage = 1.5G)
  |\
  | C (low = 1G, usage = 2.5G)
  B (low = 1G, usage = 0.5G)

 for A reclaim we have
 B.elow = B.low
 C.elow = C.low

 For the global reclaim
 A.elow = A.low
 B.elow = min(B.usage, B.low) because children_low_usage <= A.elow
 C.elow = min(C.usage, C.low)

 With the effective values resetting we have A reclaim
 A.elow = 0
 B.elow = B.low
 C.elow = C.low

 and global reclaim could see the above and then
 B.elow = C.elow = 0 because children_low_usage > A.elow

Which means that protected memcgs would get reclaimed.

In future we would like to make mem_cgroup_protected more robust against
racing reclaim contexts but that is likely more complex solution than
this simple workaround.

[hannes@cmpxchg.org - large part of the changelog]
[mhocko@suse.com - workaround explanation]
[chris@chrisdown.name - retitle]
Fixes: 9783aa9917f8 ("mm, memcg: proportional memory.{low,min} reclaim")
Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Chris Down <chris@chrisdown.name>
Acked-by: Roman Gushchin <guro@fb.com>
---
 include/linux/memcontrol.h | 42 ++++++++++++++++++++++++++++++++++++--
 mm/memcontrol.c            |  8 ++++++++
 mm/vmscan.c                |  3 ++-
 3 files changed, 50 insertions(+), 3 deletions(-)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index d275c72c4f8e..c07548ce26cb 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -344,12 +344,49 @@ static inline bool mem_cgroup_disabled(void)
 	return !cgroup_subsys_enabled(memory_cgrp_subsys);
 }
 
-static inline unsigned long mem_cgroup_protection(struct mem_cgroup *memcg,
+static inline unsigned long mem_cgroup_protection(struct mem_cgroup *root,
+						  struct mem_cgroup *memcg,
 						  bool in_low_reclaim)
 {
 	if (mem_cgroup_disabled())
 		return 0;
 
+	/*
+	 * There is no reclaim protection applied to a targeted reclaim.
+	 * We are special casing this specific case here because
+	 * mem_cgroup_protected calculation is not robust enough to keep
+	 * the protection invariant for calculated effective values for
+	 * parallel reclaimers with different reclaim target. This is
+	 * especially a problem for tail memcgs (as they have pages on LRU)
+	 * which would want to have effective values 0 for targeted reclaim
+	 * but a different value for external reclaim.
+	 *
+	 * Example
+	 * Let's have global and A's reclaim in parallel:
+	 *  |
+	 *  A (low=2G, usage = 3G, max = 3G, children_low_usage = 1.5G)
+	 *  |\
+	 *  | C (low = 1G, usage = 2.5G)
+	 *  B (low = 1G, usage = 0.5G)
+	 *
+	 * For the global reclaim
+	 * A.elow = A.low
+	 * B.elow = min(B.usage, B.low) because children_low_usage <= A.elow
+	 * C.elow = min(C.usage, C.low)
+	 *
+	 * With the effective values resetting we have A reclaim
+	 * A.elow = 0
+	 * B.elow = B.low
+	 * C.elow = C.low
+	 *
+	 * If the global reclaim races with A's reclaim then
+	 * B.elow = C.elow = 0 because children_low_usage > A.elow)
+	 * is possible and reclaiming B would be violating the protection.
+	 *
+	 */
+	if (root == memcg)
+		return 0;
+
 	if (in_low_reclaim)
 		return READ_ONCE(memcg->memory.emin);
 
@@ -835,7 +872,8 @@ static inline void memcg_memory_event_mm(struct mm_struct *mm,
 {
 }
 
-static inline unsigned long mem_cgroup_protection(struct mem_cgroup *memcg,
+static inline unsigned long mem_cgroup_protection(struct mem_cgroup *root,
+						  struct mem_cgroup *memcg,
 						  bool in_low_reclaim)
 {
 	return 0;
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 5beea03dd58a..1206682edc1a 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -6388,6 +6388,14 @@ enum mem_cgroup_protection mem_cgroup_protected(struct mem_cgroup *root,
 
 	if (!root)
 		root = root_mem_cgroup;
+
+	/*
+	 * Effective values of the reclaim targets are ignored so they
+	 * can be stale. Have a look at mem_cgroup_protection for more
+	 * details.
+	 * TODO: calculation should be more robust so that we do not need
+	 * that special casing.
+	 */
 	if (memcg == root)
 		return MEMCG_PROT_NONE;
 
diff --git a/mm/vmscan.c b/mm/vmscan.c
index b06868fc4926..4d3027ac131c 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2346,7 +2346,8 @@ static void get_scan_count(struct lruvec *lruvec, struct scan_control *sc,
 		unsigned long protection;
 
 		lruvec_size = lruvec_lru_size(lruvec, lru, sc->reclaim_idx);
-		protection = mem_cgroup_protection(memcg,
+		protection = mem_cgroup_protection(sc->target_mem_cgroup,
+						   memcg,
 						   sc->memcg_low_reclaim);
 
 		if (protection) {
-- 
2.18.2

[PATCH v3 2/2] mm, memcg: Decouple e{low,min} state mutations from protection checks

[Yafang Shao]

From: Chris Down <chris@chrisdown.name>

mem_cgroup_protected currently is both used to set effective low and min
and return a mem_cgroup_protection based on the result.  As a user, this
can be a little unexpected: it appears to be a simple predicate function,
if not for the big warning in the comment above about the order in which
it must be executed.

This change makes it so that we separate the state mutations from the
actual protection checks, which makes it more obvious where we need to be
careful mutating internal state, and where we are simply checking and
don't need to worry about that.

Signed-off-by: Chris Down <chris@chrisdown.name>
Suggested-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Roman Gushchin <guro@fb.com>
Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
---
 include/linux/memcontrol.h | 43 ++++++++++++++++++++++++++++----------
 mm/memcontrol.c            | 28 +++++++------------------
 mm/vmscan.c                | 17 ++++-----------
 3 files changed, 43 insertions(+), 45 deletions(-)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index c07548ce26cb..7a2c56fc220c 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -50,12 +50,6 @@ enum memcg_memory_event {
 	MEMCG_NR_MEMORY_EVENTS,
 };
 
-enum mem_cgroup_protection {
-	MEMCG_PROT_NONE,
-	MEMCG_PROT_LOW,
-	MEMCG_PROT_MIN,
-};
-
 struct mem_cgroup_reclaim_cookie {
 	pg_data_t *pgdat;
 	unsigned int generation;
@@ -394,8 +388,26 @@ static inline unsigned long mem_cgroup_protection(struct mem_cgroup *root,
 		   READ_ONCE(memcg->memory.elow));
 }
 
-enum mem_cgroup_protection mem_cgroup_protected(struct mem_cgroup *root,
-						struct mem_cgroup *memcg);
+void mem_cgroup_calculate_protection(struct mem_cgroup *root,
+				     struct mem_cgroup *memcg);
+
+static inline bool mem_cgroup_below_low(struct mem_cgroup *memcg)
+{
+	if (mem_cgroup_disabled())
+		return false;
+
+	return READ_ONCE(memcg->memory.elow) >=
+		page_counter_read(&memcg->memory);
+}
+
+static inline bool mem_cgroup_below_min(struct mem_cgroup *memcg)
+{
+	if (mem_cgroup_disabled())
+		return false;
+
+	return READ_ONCE(memcg->memory.emin) >=
+		page_counter_read(&memcg->memory);
+}
 
 int mem_cgroup_try_charge(struct page *page, struct mm_struct *mm,
 			  gfp_t gfp_mask, struct mem_cgroup **memcgp,
@@ -879,10 +891,19 @@ static inline unsigned long mem_cgroup_protection(struct mem_cgroup *root,
 	return 0;
 }
 
-static inline enum mem_cgroup_protection mem_cgroup_protected(
-	struct mem_cgroup *root, struct mem_cgroup *memcg)
+static inline void mem_cgroup_calculate_protection(struct mem_cgroup *root,
+						   struct mem_cgroup *memcg)
+{
+}
+
+static inline bool mem_cgroup_below_low(struct mem_cgroup *memcg)
 {
-	return MEMCG_PROT_NONE;
+	return false;
+}
+
+static inline bool mem_cgroup_below_min(struct mem_cgroup *memcg)
+{
+	return false;
 }
 
 static inline int mem_cgroup_try_charge(struct page *page, struct mm_struct *mm,
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 1206682edc1a..474815acaf93 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -6370,21 +6370,15 @@ static unsigned long effective_protection(unsigned long usage,
  *
  * WARNING: This function is not stateless! It can only be used as part
  *          of a top-down tree iteration, not for isolated queries.
- *
- * Returns one of the following:
- *   MEMCG_PROT_NONE: cgroup memory is not protected
- *   MEMCG_PROT_LOW: cgroup memory is protected as long there is
- *     an unprotected supply of reclaimable memory from other cgroups.
- *   MEMCG_PROT_MIN: cgroup memory is protected
  */
-enum mem_cgroup_protection mem_cgroup_protected(struct mem_cgroup *root,
-						struct mem_cgroup *memcg)
+void mem_cgroup_calculate_protection(struct mem_cgroup *root,
+				     struct mem_cgroup *memcg)
 {
 	unsigned long usage, parent_usage;
 	struct mem_cgroup *parent;
 
 	if (mem_cgroup_disabled())
-		return MEMCG_PROT_NONE;
+		return;
 
 	if (!root)
 		root = root_mem_cgroup;
@@ -6397,21 +6391,21 @@ enum mem_cgroup_protection mem_cgroup_protected(struct mem_cgroup *root,
 	 * that special casing.
 	 */
 	if (memcg == root)
-		return MEMCG_PROT_NONE;
+		return;
 
 	usage = page_counter_read(&memcg->memory);
 	if (!usage)
-		return MEMCG_PROT_NONE;
+		return;
 
 	parent = parent_mem_cgroup(memcg);
 	/* No parent means a non-hierarchical mode on v1 memcg */
 	if (!parent)
-		return MEMCG_PROT_NONE;
+		return;
 
 	if (parent == root) {
 		memcg->memory.emin = READ_ONCE(memcg->memory.min);
 		memcg->memory.elow = memcg->memory.low;
-		goto out;
+		return;
 	}
 
 	parent_usage = page_counter_read(&parent->memory);
@@ -6424,14 +6418,6 @@ enum mem_cgroup_protection mem_cgroup_protected(struct mem_cgroup *root,
 	WRITE_ONCE(memcg->memory.elow, effective_protection(usage, parent_usage,
 			memcg->memory.low, READ_ONCE(parent->memory.elow),
 			atomic_long_read(&parent->memory.children_low_usage)));
-
-out:
-	if (usage <= memcg->memory.emin)
-		return MEMCG_PROT_MIN;
-	else if (usage <= memcg->memory.elow)
-		return MEMCG_PROT_LOW;
-	else
-		return MEMCG_PROT_NONE;
 }
 
 /**
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 4d3027ac131c..c71660e2c304 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2635,14 +2635,15 @@ static void shrink_node_memcgs(pg_data_t *pgdat, struct scan_control *sc)
 		unsigned long reclaimed;
 		unsigned long scanned;
 
-		switch (mem_cgroup_protected(target_memcg, memcg)) {
-		case MEMCG_PROT_MIN:
+		mem_cgroup_calculate_protection(target_memcg, memcg);
+
+		if (mem_cgroup_below_min(memcg)) {
 			/*
 			 * Hard protection.
 			 * If there is no reclaimable memory, OOM.
 			 */
 			continue;
-		case MEMCG_PROT_LOW:
+		} else if (mem_cgroup_below_low(memcg)) {
 			/*
 			 * Soft protection.
 			 * Respect the protection only as long as
@@ -2654,16 +2655,6 @@ static void shrink_node_memcgs(pg_data_t *pgdat, struct scan_control *sc)
 				continue;
 			}
 			memcg_memory_event(memcg, MEMCG_LOW);
-			break;
-		case MEMCG_PROT_NONE:
-			/*
-			 * All protection thresholds breached. We may
-			 * still choose to vary the scan pressure
-			 * applied based on by how much the cgroup in
-			 * question has exceeded its protection
-			 * thresholds (see get_scan_count).
-			 */
-			break;
 		}
 
 		reclaimed = sc->nr_reclaimed;
-- 
2.18.2

Re: [PATCH v3 2/2] mm, memcg: Decouple e{low,min} state mutations from protection checks

[Naresh Kamboju]

On Tue, 5 May 2020 at 14:12, Yafang Shao <laoar.shao@gmail.com> wrote:
>
> From: Chris Down <chris@chrisdown.name>
>
> mem_cgroup_protected currently is both used to set effective low and min
> and return a mem_cgroup_protection based on the result.  As a user, this
> can be a little unexpected: it appears to be a simple predicate function,
> if not for the big warning in the comment above about the order in which
> it must be executed.
>
> This change makes it so that we separate the state mutations from the
> actual protection checks, which makes it more obvious where we need to be
> careful mutating internal state, and where we are simply checking and
> don't need to worry about that.

This patch is causing oom-killer while running mkfs -t ext4 on i386 kernel
running on x86_64 machine version linux-next 5.7.0-rc6-next-20200521.

+ mkfs -t ext4 /dev/disk/by-id/ata-TOSHIBA_MG04ACA100N_Y8RQK14KF6XF
mke2fs 1.43.8 (1-Jan-2018)
Creating filesystem with 244190646 4k blocks and 61054976 inodes
Filesystem UUID: 5309a579-5f29-4e9e-959d-0cb1da3490a8
Superblock backups stored on blocks:
32768, 98304, 163840, 229376, 294912, 819200, 884736, 1605632, 2654208,
4096000, 7962624, 11239424, 20480000, 23887872, 71663616, 78675968,
102400000, 214990848
Allocating group tables:    0/7453                           done
Writing inode tables:    0/7453                           done
Creating journal (262144 blocks): [   35.419377] mkfs.ext4 invoked
oom-killer: gfp_mask=0x101cc0(GFP_USER|__GFP_WRITE), order=0,
oom_score_adj=0
[   35.429138] CPU: 2 PID: 391 Comm: mkfs.ext4 Not tainted
5.7.0-rc6-next-20200521 #1
[   35.436707] Hardware name: Supermicro SYS-5019S-ML/X11SSH-F, BIOS
2.2 05/23/2018
[   35.444099] Call Trace:
[   35.446558]  dump_stack+0x54/0x6e
[   35.449874]  dump_header+0x3d/0x1d2
[   35.453364]  ? oom_badness.part.0+0x11/0x120
[   35.457635]  ? ___ratelimit+0x8f/0xdc
[   35.461301]  oom_kill_process.cold+0x9/0xe
[   35.465390]  out_of_memory+0x1b1/0x260
[   35.469135]  __alloc_pages_nodemask+0xe1d/0xed0
[   35.473658]  ? alloc_page_buffers+0x81/0x130
[   35.477923]  pagecache_get_page+0xae/0x260
[   35.482014]  grab_cache_page_write_begin+0x1c/0x30
[   35.486798]  block_write_begin+0x1e/0x90
[   35.490716]  blkdev_write_begin+0x1e/0x20
[   35.494719]  ? bdev_evict_inode+0xd0/0xd0
[   35.498722]  generic_perform_write+0x97/0x180
[   35.503073]  __generic_file_write_iter+0x140/0x1f0
[   35.507857]  blkdev_write_iter+0xc0/0x190
[   35.511860]  __vfs_write+0x132/0x1e0
[   35.515431]  vfs_write+0xa1/0x1a0
[   35.518742]  ksys_pwrite64+0x50/0x80
[   35.522315]  __ia32_sys_ia32_pwrite64+0x16/0x20
[   35.526845]  do_syscall_32_irqs_on+0x3d/0x250
[   35.531195]  ? do_user_addr_fault+0x1a0/0x3c0
[   35.535548]  ? __prepare_exit_to_usermode+0x50/0x1a0
[   35.540504]  do_fast_syscall_32+0x39/0xb0
[   35.544508]  entry_SYSENTER_32+0xa5/0xf8
[   35.548426] EIP: 0xb7efb549
[   35.551218] Code: 03 74 c0 01 10 05 03 74 b8 01 10 06 03 74 b4 01
10 07 03 74 b0 01 10 08 03 74 d8 01 00 00 00 00 00 51 52 55 89 e5 0f
34 cd 80 <5d> 5a 59 c3 90 90 90 90 8d 76 00 58 b8 77 00 00 00 cd 80 90
8d 76
[   35.569962] EAX: ffffffda EBX: 00000003 ECX: b77ef010 EDX: 00400000
[   35.576217] ESI: 38400000 EDI: 00000074 EBP: 07438400 ESP: bfdff180
[   35.582476] DS: 007b ES: 007b FS: 0000 GS: 0033 SS: 007b EFLAGS: 00000246
[   35.589260] Mem-Info:
[   35.591552] active_anon:5403 inactive_anon:2167 isolated_anon:0
[   35.591552]  active_file:4174 inactive_file:212518 isolated_file:0
[   35.591552]  unevictable:0 dirty:16699 writeback:6001 unstable:0
[   35.591552]  slab_reclaimable:5868 slab_unreclaimable:3494
[   35.591552]  mapped:6285 shmem:2236 pagetables:176 bounce:0
[   35.591552]  free:264050 free_pcp:1186 free_cma:0
[   35.625311] Node 0 active_anon:21612kB inactive_anon:8668kB
active_file:16696kB inactive_file:850072kB unevictable:0kB
isolated(anon):0kB isolated(file):0kB mapped:25140kB dirty:62704kB
writeback:22764kB shmem:8944kB writeback_tmp:0kB unstable:0kB
all_unreclaimable? yes
[   35.649169] DMA free:3360kB min:68kB low:84kB high:100kB
reserved_highatomic:0KB active_anon:0kB inactive_anon:0kB
active_file:0kB inactive_file:12012kB unevictable:0kB
writepending:12012kB present:15964kB managed:15876kB mlocked:0kB
kernel_stack:0kB pagetables:0kB bounce:0kB free_pcp:0kB local_pcp:0kB
free_cma:0kB
[   35.677015] lowmem_reserve[]: 0 824 1947 824
[   35.681286] Normal free:4300kB min:7732kB low:8640kB high:9548kB
reserved_highatomic:0KB active_anon:0kB inactive_anon:0kB
active_file:1132kB inactive_file:786452kB unevictable:0kB
writepending:64032kB present:884728kB managed:845292kB mlocked:0kB
kernel_stack:1112kB pagetables:0kB bounce:0kB free_pcp:2392kB
local_pcp:456kB free_cma:0kB
[   35.711109] lowmem_reserve[]: 0 0 8980 0
[   35.715051] HighMem free:1048740kB min:512kB low:1748kB high:2984kB
reserved_highatomic:0KB active_anon:21612kB inactive_anon:8668kB
active_file:15564kB inactive_file:51556kB unevictable:0kB
writepending:0kB present:1149540kB managed:1149540kB mlocked:0kB
kernel_stack:0kB pagetables:704kB bounce:0kB free_pcp:2216kB
local_pcp:200kB free_cma:0kB
[   35.745418] lowmem_reserve[]: 0 0 0 0
[   35.749117] DMA: 7*4kB (UE) 1*8kB (U) 2*16kB (UE) 1*32kB (E) 1*64kB
(E) 1*128kB (E) 0*256kB 0*512kB 1*1024kB (E) 1*2048kB (E) 0*4096kB =
3364kB
[   35.762006] Normal: 19*4kB (U) 18*8kB (UE) 18*16kB (UE) 12*32kB
(UE) 6*64kB (U) 2*128kB (U) 2*256kB (UE) 1*512kB (E) 0*1024kB 1*2048kB
(U) 0*4096kB = 4604kB
[   35.776020] HighMem: 1*4kB (U) 0*8kB 0*16kB 1*32kB (M) 0*64kB
1*128kB (M) 0*256kB 0*512kB 0*1024kB 0*2048kB 256*4096kB (M) =
1048740kB
[   35.788093] Node 0 hugepages_total=0 hugepages_free=0
hugepages_surp=0 hugepages_size=4096kB
[   35.796533] 218903 total pagecache pages
[   35.800503] 0 pages in swap cache
[   35.803873] Swap cache stats: add 0, delete 0, find 0/0
[   35.809145] Free swap  = 0kB
[   35.812083] Total swap = 0kB
[   35.815021] 512558 pages RAM
[   35.817957] 287385 pages HighMem/MovableOnly
[   35.822221] 9881 pages reserved
[   35.825368] Tasks state (memory values in pages):
[   35.830124] [  pid  ]   uid  tgid total_vm      rss pgtables_bytes
swapents oom_score_adj name
[   35.838791] [    225]     0   225     3425     1294    24576
0             0 systemd-journal
[   35.847868] [    240]     0   240     3326      868    20480
0         -1000 systemd-udevd
[   35.856785] [    243]   994   243     3929      450    24576
0             0 systemd-timesyn
[   35.865874] [    260]   993   260     1569      786    20480
0             0 systemd-network
[   35.874966] [    278]   992   278     1729      843    20480
0             0 systemd-resolve
[   35.884007] [    282]     0   282      809      428    16384
0             0 crond
[   35.892229] [    283]     0   283     2032     1104    20480
0             0 haveged
[   35.900635] [    284]     0   284      922      194    16384
0             0 klogd
[   35.908820] [    285]     0   285     5638     1481    32768
0             0 thermald
[   35.917304] [    286]   995   286     1182      664    20480
0             0 avahi-daemon
[   35.926133] [    287]   996   287     1174      835    24576
0          -900 dbus-daemon
[   35.934880] [    288]   995   288     1182       58    20480
0             0 avahi-daemon
[   35.943710] [    289]     0   289      921      409    16384
0             0 syslogd
[   35.952108] [    290]     0   290     1468      998    20480
0             0 systemd-logind
[   35.961060] [    303]     0   303      594       15    16384
0             0 acpid
[   35.969275] [    304]     0   304    11786     2635    45056
0             0 NetworkManager
[   35.978282] [    305]     0   305      677      429    16384
0             0 atd
[   35.986280] [    323]     0   323     1347      321    20480
0             0 systemd-hostnam
[   35.995318] [    334] 65534   334      729       32    16384
0             0 dnsmasq
[   36.003708] [    335]     0   335      666      443    16384
0             0 agetty
[   36.012019] [    336]     0   336      947      710    20480
0             0 login
[   36.020246] [    337]     0   337      666      419    16384
0             0 agetty
[   36.028555] [    348]   998   348    19521     2782    65536
0             0 polkitd
[   36.036901] [    356]     0   356     1892     1183    20480
0             0 systemd
[   36.045300] [    357]     0   357     2320      316    20480
0             0 (sd-pam)
[   36.053731] [    361]     0   361      971      721    16384
0             0 sh
[   36.061698] [    365]     0   365      920      610    16384
0             0 su
[   36.069682] [    366]     0   366      971      689    16384
0             0 sh
[   36.077664] [    371]     0   371      903      580    16384
0             0 lava-test-runne
[   36.086761] [    381]     0   381      903      520    16384
0             0 lava-test-shell
[   36.095852] [    382]     0   382      903      581    16384
0             0 sh
[   36.103816] [    391]     0   391     1976     1688    24576
0             0 mkfs.ext4
[   36.112336] oom-kill:constraint=CONSTRAINT_NONE,nodemask=(null),cpuset=/,mems_allowed=0,global_oom,task_memcg=/,task=polkitd,pid=348,uid=998
[   36.125003] Out of memory: Killed process 348 (polkitd)
total-vm:78084kB, anon-rss:2980kB, file-rss:8148kB, shmem-rss:0kB,
UID:998 pgtables:64kB oom_score_adj:0
[   36.139810] oom_reaper: reaped process 348 (polkitd), now
anon-rss:0kB, file-rss:0kB, shmem-rss:0kB
[   36.148879] mkfs.ext4 invoked oom-killer:
gfp_mask=0x101cc0(GFP_USER|__GFP_WRITE), order=0, oom_score_adj=0
[   36.158626] CPU: 1 PID: 391 Comm: mkfs.ext4 Not tainted
5.7.0-rc6-next-20200521 #1
[   36.166220] Hardware name: Supermicro SYS-5019S-ML/X11SSH-F, BIOS
2.2 05/23/2018
[   36.173604] Call Trace:
[   36.176050]  dump_stack+0x54/0x6e
[   36.179360]  dump_header+0x3d/0x1d2
[   36.182844]  ? oom_badness.part.0+0x11/0x120
[   36.187110]  ? ___ratelimit+0x8f/0xdc
[   36.190773]  oom_kill_process.cold+0x9/0xe
[   36.194863]  out_of_memory+0x1b1/0x260
[   36.198610]  __alloc_pages_nodemask+0xe1d/0xed0
[   36.203141]  ? alloc_page_buffers+0x81/0x130
[   36.207406]  pagecache_get_page+0xae/0x260
[   36.211496]  grab_cache_page_write_begin+0x1c/0x30
[   36.216281]  block_write_begin+0x1e/0x90
[   36.220197]  blkdev_write_begin+0x1e/0x20
[   36.224201]  ? bdev_evict_inode+0xd0/0xd0
[   36.228205]  generic_perform_write+0x97/0x180
[   36.232557]  __generic_file_write_iter+0x140/0x1f0
[   36.237340]  blkdev_write_iter+0xc0/0x190
[   36.241344]  __vfs_write+0x132/0x1e0
[   36.244915]  vfs_write+0xa1/0x1a0
[   36.248225]  ksys_pwrite64+0x50/0x80
[   36.251797]  __ia32_sys_ia32_pwrite64+0x16/0x20
[   36.256319]  do_syscall_32_irqs_on+0x3d/0x250
[   36.260693]  ? do_user_addr_fault+0x1a0/0x3c0
[   36.265045]  ? __prepare_exit_to_usermode+0x50/0x1a0
[   36.270004]  do_fast_syscall_32+0x39/0xb0
[   36.274006]  entry_SYSENTER_32+0xa5/0xf8
[   36.277926] EIP: 0xb7efb549
[   36.280728] Code: 03 74 c0 01 10 05 03 74 b8 01 10 06 03 74 b4 01
10 07 03 74 b0 01 10 08 03 74 d8 01 00 00 00 00 00 51 52 55 89 e5 0f
34 cd 80 <5d> 5a 59 c3 90 90 90 90 8d 76 00 58 b8 77 00 00 00 cd 80 90
8d 76
[   36.299471] EAX: ffffffda EBX: 00000003 ECX: b77ef010 EDX: 00400000
[   36.305728] ESI: 38400000 EDI: 00000074 EBP: 07438400 ESP: bfdff180
[   36.311986] DS: 007b ES: 007b FS: 0000 GS: 0033 SS: 007b EFLAGS: 00000246
[   36.318783] Mem-Info:
[   36.321070] active_anon:4659 inactive_anon:2167 isolated_anon:0
[   36.321070]  active_file:4639 inactive_file:212058 isolated_file:0
[   36.321070]  unevictable:0 dirty:14286 writeback:23 unstable:0
[   36.321070]  slab_reclaimable:5883 slab_unreclaimable:3313
[   36.321070]  mapped:5709 shmem:2236 pagetables:176 bounce:0
[   36.321070]  free:264784 free_pcp:1341 free_cma:0
[   36.354669] Node 0 active_anon:18636kB inactive_anon:8668kB
active_file:18556kB inactive_file:848232kB unevictable:0kB
isolated(anon):0kB isolated(file):0kB mapped:22836kB dirty:57144kB
writeback:92kB shmem:8944kB writeback_tmp:0kB unstable:0kB
all_unreclaimable? yes
[   36.378296] DMA free:3364kB min:68kB low:84kB high:100kB
reserved_highatomic:0KB active_anon:0kB inactive_anon:0kB
active_file:0kB inactive_file:12124kB unevictable:0kB
writepending:12132kB present:15964kB managed:15876kB mlocked:0kB
kernel_stack:0kB pagetables:0kB bounce:0kB free_pcp:0kB local_pcp:0kB
free_cma:0kB
[   36.406167] lowmem_reserve[]: 0 824 1947 824
[   36.410467] Normal free:4552kB min:7732kB low:8640kB high:9548kB
reserved_highatomic:0KB active_anon:0kB inactive_anon:0kB
active_file:1132kB inactive_file:786524kB unevictable:0kB
writepending:45100kB present:884728kB managed:845292kB mlocked:0kB
kernel_stack:1112kB pagetables:0kB bounce:0kB free_pcp:2548kB
local_pcp:1432kB free_cma:0kB
[   36.440330] lowmem_reserve[]: 0 0 8980 0
[   36.444274] HighMem free:1051220kB min:512kB low:1748kB high:2984kB
reserved_highatomic:0KB active_anon:18636kB inactive_anon:8668kB
active_file:17424kB inactive_file:49696kB unevictable:0kB
writepending:0kB present:1149540kB managed:1149540kB mlocked:0kB
kernel_stack:0kB pagetables:704kB bounce:0kB free_pcp:2812kB
local_pcp:516kB free_cma:0kB
[   36.474680] lowmem_reserve[]: 0 0 0 0
[   36.478401] DMA: 3*4kB (U) 1*8kB (U) 1*16kB (U) 0*32kB 2*64kB (UE)
1*128kB (E) 0*256kB 0*512kB 1*1024kB (E) 1*2048kB (E) 0*4096kB =
3364kB
[   36.490847] Normal: 19*4kB (U) 22*8kB (UE) 19*16kB (UE) 13*32kB
(UE) 6*64kB (U) 2*128kB (U) 2*256kB (UE) 1*512kB (E) 0*1024kB 1*2048kB
(U) 0*4096kB = 4684kB
[   36.504851] HighMem: 119*4kB (UM) 48*8kB (M) 12*16kB (UM) 11*32kB
(M) 8*64kB (UM) 6*128kB (M) 0*256kB 0*512kB 0*1024kB 0*2048kB
256*4096kB (M) = 1051260kB
[   36.518695] Node 0 hugepages_total=0 hugepages_free=0
hugepages_surp=0 hugepages_size=4096kB
[   36.527151] 218965 total pagecache pages
[   36.531095] 0 pages in swap cache
[   36.534430] Swap cache stats: add 0, delete 0, find 0/0
[   36.539697] Free swap  = 0kB
[   36.542602] Total swap = 0kB
[   36.545531] 512558 pages RAM
[   36.548436] 287385 pages HighMem/MovableOnly
[   36.552729] 9881 pages reserved
[   36.555897] Tasks state (memory values in pages):
[   36.560621] [  pid  ]   uid  tgid total_vm      rss pgtables_bytes
swapents oom_score_adj name
[   36.569230] [    225]     0   225     3425     1294    28672
0             0 systemd-journal
[   36.578295] [    240]     0   240     3326      868    20480
0         -1000 systemd-udevd
[   36.587186] [    243]   994   243     3929      450    24576
0             0 systemd-timesyn
[   36.596249] [    260]   993   260     1569      786    20480
0             0 systemd-network
[   36.605307] [    278]   992   278     1729      843    20480
0             0 systemd-resolve
[   36.614363] [    282]     0   282      809      428    16384
0             0 crond
[   36.622551] [    283]     0   283     2032     1104    20480
0             0 haveged
[   36.630918] [    284]     0   284      922      194    16384
0             0 klogd
[   36.639114] [    285]     0   285     5638     1481    32768
0             0 thermald
[   36.647563] [    286]   995   286     1182      664    20480
0             0 avahi-daemon
[   36.656362] [    287]   996   287     1174      835    24576
0          -900 dbus-daemon
[   36.665081] [    288]   995   288     1182       58    20480
0             0 avahi-daemon
[   36.673884] [    289]     0   289      921      409    16384
0             0 syslogd
[   36.682249] [    290]     0   290     1468      998    20480
0             0 systemd-logind
[   36.691228] [    303]     0   303      594       15    16384
0             0 acpid
[   36.699425] [    304]     0   304    11786     2635    45056
0             0 NetworkManager
[   36.708395] [    305]     0   305      677      429    16384
0             0 atd
[   36.716394] [    323]     0   323     1347      321    20480
0             0 systemd-hostnam
[   36.725435] [    334] 65534   334      729       32    16384
0             0 dnsmasq
[   36.733781] [    335]     0   335      666      443    16384
0             0 agetty
[   36.742041] [    336]     0   336      947      710    20480
0             0 login
[   36.750237] [    337]     0   337      666      419    16384
0             0 agetty
[   36.758514] [    356]     0   356     1892     1183    20480
0             0 systemd
[   36.766877] [    357]     0   357     2320      316    20480
0             0 (sd-pam)
[   36.775326] [    361]     0   361      971      721    16384
0             0 sh
[   36.783257] [    365]     0   365      920      610    16384
0             0 su
[   36.791170] [    366]     0   366      971      689    16384
0             0 sh
[   36.799082] [    371]     0   371      903      580    16384
0             0 lava-test-runne
[   36.808122] [    381]     0   381      903      520    16384
0             0 lava-test-shell
[   36.817161] [    382]     0   382      903      581    16384
0             0 sh
[   36.825073] [    391]     0   391     1976     1688    24576
0             0 mkfs.ext4
[   36.833591] oom-kill:constraint=CONSTRAINT_NONE,nodemask=(null),cpuset=/,mems_allowed=0,global_oom,task_memcg=/,task=NetworkManager,pid=304,uid=0
[   36.846621] Out of memory: Killed process 304 (NetworkManager)
total-vm:47144kB, anon-rss:1396kB, file-rss:9144kB, shmem-rss:0kB,
UID:0 pgtables:44kB oom_score_adj:0
[   36.861729] oom_reaper: reaped process 304 (NetworkManager), now
anon-rss:0kB, file-rss:0kB, shmem-rss:0kB
[   36.861738] klogd invoked oom-killer:
gfp_mask=0xc2cc0(GFP_KERNEL|__GFP_NOWARN|__GFP_COMP|__GFP_NOMEMALLOC),
order=0, oom_score_adj=0
[   36.883368] CPU: 2 PID: 284 Comm: klogd Not tainted
5.7.0-rc6-next-20200521 #1
[   36.890607] Hardware name: Supermicro SYS-5019S-ML/X11SSH-F, BIOS
2.2 05/23/2018
[   36.897992] Call Trace:
[   36.900438]  dump_stack+0x54/0x6e
[   36.903763]  dump_header+0x3d/0x1d2
[   36.907247]  ? oom_badness.part.0+0x11/0x120
[   36.911510]  ? ___ratelimit+0x8f/0xdc
[   36.915167]  oom_kill_process.cold+0x9/0xe
[   36.919258]  out_of_memory+0x1b1/0x260
[   36.923005]  __alloc_pages_nodemask+0xe1d/0xed0
[   36.927537]  alloc_slab_page+0x13d/0x2c0
[   36.931453]  new_slab+0x22e/0x280
[   36.934766]  ? cpumask_next_and+0x18/0x20
[   36.938777]  ___slab_alloc.constprop.0+0x248/0x4a0
[   36.943563]  ? __alloc_skb+0x64/0x1a0
[   36.947228]  ? __alloc_skb+0x41/0x1a0
[   36.950885]  __slab_alloc.constprop.0+0xf/0x20
[   36.955321]  ? __slab_alloc.constprop.0+0xf/0x20
[   36.959932]  __kmalloc_track_caller+0x23e/0x270
[   36.964456]  ? __alloc_skb+0x64/0x1a0
[   36.968114]  ? _cond_resched+0x12/0x30
[   36.971857]  __kmalloc_reserve.isra.0+0x1d/0x70
[   36.976380]  __alloc_skb+0x64/0x1a0
[   36.979866]  ? update_rq_clock.part.0+0x16/0xe0
[   36.984389]  alloc_skb_with_frags+0x3b/0x1a0
[   36.988665]  sock_alloc_send_pskb+0x1c7/0x1f0
[   36.993040]  ? selinux_inet_conn_established+0x40/0x40
[   36.998179]  unix_dgram_sendmsg+0x12a/0x690
[   37.002365]  ? selinux_socket_recvmsg+0x20/0x20
[   37.006897]  ? unix_dgram_connect+0x2f0/0x2f0
[   37.011247]  sock_sendmsg+0x5c/0x60
[   37.014730]  __sys_sendto+0xe1/0x120
[   37.018301]  ? msg_print_text+0x80/0x1c0
[   37.022219]  ? do_syslog+0x19c/0x940
[   37.025788]  ? do_syslog+0x878/0x940
[   37.029358]  ? do_syslog+0x878/0x940
[   37.032931]  ? kunmap_atomic_high+0x4e/0x58
[   37.037109]  ? handle_mm_fault+0x25c/0xc60
[   37.041209]  __ia32_sys_socketcall+0x29f/0x330
[   37.045665]  do_syscall_32_irqs_on+0x3d/0x250
[   37.050038]  ? do_user_addr_fault+0x1a0/0x3c0
[   37.054388]  ? __prepare_exit_to_usermode+0x50/0x1a0
[   37.059346]  do_fast_syscall_32+0x39/0xb0
[   37.063351]  entry_SYSENTER_32+0xa5/0xf8
[   37.067276] EIP: 0xb7f66549

ref:
https://lkft.validation.linaro.org/scheduler/job/1444120#L1220

-- 
Linaro LKFT
https://lkft.linaro.org

Re: [PATCH v3 2/2] mm, memcg: Decouple e{low,min} state mutations from protection checks

[Chris Down]

Naresh Kamboju writes:
>This patch is causing oom-killer while running mkfs -t ext4 on i386 kernel
>running on x86_64 machine version linux-next 5.7.0-rc6-next-20200521.

I think I see what's wrong here -- if we bail out early, memory.e{min,low} 
might be uninitialised.

Does this patch fix it, by any chance?

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index d3b23c57bed4..aa902b9cbb79 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -5046,6 +5046,9 @@ mem_cgroup_css_alloc(struct cgroup_subsys_state *parent_css)
  			memory_cgrp_subsys.broken_hierarchy = true;
  	}
  
+	memcg->memory.emin = 0;
+	memcg->memory.elow = 0;
+
  	/* The following stuff does not apply to the root */
  	if (!parent) {
  #ifdef CONFIG_MEMCG_KMEM
-- 
2.26.2

Re: [PATCH v3 2/2] mm, memcg: Decouple e{low,min} state mutations from protection checks

[Naresh Kamboju]

On Fri, 22 May 2020 at 17:15, Chris Down <chris@chrisdown.name> wrote:
>
> Naresh Kamboju writes:
> >This patch is causing oom-killer while running mkfs -t ext4 on i386 kernel
> >running on x86_64 machine version linux-next 5.7.0-rc6-next-20200521.
>
> I think I see what's wrong here -- if we bail out early, memory.e{min,low}
> might be uninitialised.
>
> Does this patch fix it, by any chance?
>
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index d3b23c57bed4..aa902b9cbb79 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -5046,6 +5046,9 @@ mem_cgroup_css_alloc(struct cgroup_subsys_state *parent_css)
>                         memory_cgrp_subsys.broken_hierarchy = true;
>         }
>
> +       memcg->memory.emin = 0;
> +       memcg->memory.elow = 0;
> +
>         /* The following stuff does not apply to the root */
>         if (!parent) {
>   #ifdef CONFIG_MEMCG_KMEM

This patch did not fix the problem.
The test log showing oom-killer link,
https://lkft.validation.linaro.org/scheduler/job/1445128#L1194

Build images:
https://builds.tuxbuild.com/YqW37GVsCHf8ndxOT2z1iQ/

- Naresh

Re: [PATCH v3 2/2] mm, memcg: Decouple e{low,min} state mutations from protection checks

[Yafang Shao]

On Fri, May 22, 2020 at 7:01 PM Naresh Kamboju
<naresh.kamboju@linaro.org> wrote:
>
> On Tue, 5 May 2020 at 14:12, Yafang Shao <laoar.shao@gmail.com> wrote:
> >
> > From: Chris Down <chris@chrisdown.name>
> >
> > mem_cgroup_protected currently is both used to set effective low and min
> > and return a mem_cgroup_protection based on the result.  As a user, this
> > can be a little unexpected: it appears to be a simple predicate function,
> > if not for the big warning in the comment above about the order in which
> > it must be executed.
> >
> > This change makes it so that we separate the state mutations from the
> > actual protection checks, which makes it more obvious where we need to be
> > careful mutating internal state, and where we are simply checking and
> > don't need to worry about that.
>
> This patch is causing oom-killer while running mkfs -t ext4 on i386 kernel
> running on x86_64 machine version linux-next 5.7.0-rc6-next-20200521.
>

Hi Narash,

Thanks for your report.
My suggestion to the issue found by you is reverting this bad commit.

As I have explained earlier in another mail thread [1] that the usage
around memcg->{emin, elow} is very buggy.
We shouldn't use memcg->{emin, elow} in the reclaim context directly,
because  these two values can be modified by many reclaimers, so the
good usage of it is storing the protection value into the
scan_control. IOW, different reclaimers have different protection.
But unfortunately my suggestion is ignored.

We can set them to 0 before using them to workaround the issue found
by you, but the fact is that we will introduce a new issue once we fix
an old issue.

[1]. https://lore.kernel.org/linux-mm/20200425152418.28388-1-laoar.shao@gmail.com/

> + mkfs -t ext4 /dev/disk/by-id/ata-TOSHIBA_MG04ACA100N_Y8RQK14KF6XF
> mke2fs 1.43.8 (1-Jan-2018)
> Creating filesystem with 244190646 4k blocks and 61054976 inodes
> Filesystem UUID: 5309a579-5f29-4e9e-959d-0cb1da3490a8
> Superblock backups stored on blocks:
> 32768, 98304, 163840, 229376, 294912, 819200, 884736, 1605632, 2654208,
> 4096000, 7962624, 11239424, 20480000, 23887872, 71663616, 78675968,
> 102400000, 214990848
> Allocating group tables:    0/7453                           done
> Writing inode tables:    0/7453                           done
> Creating journal (262144 blocks): [   35.419377] mkfs.ext4 invoked
> oom-killer: gfp_mask=0x101cc0(GFP_USER|__GFP_WRITE), order=0,
> oom_score_adj=0
> [   35.429138] CPU: 2 PID: 391 Comm: mkfs.ext4 Not tainted
> 5.7.0-rc6-next-20200521 #1
> [   35.436707] Hardware name: Supermicro SYS-5019S-ML/X11SSH-F, BIOS
> 2.2 05/23/2018
> [   35.444099] Call Trace:
> [   35.446558]  dump_stack+0x54/0x6e
> [   35.449874]  dump_header+0x3d/0x1d2
> [   35.453364]  ? oom_badness.part.0+0x11/0x120
> [   35.457635]  ? ___ratelimit+0x8f/0xdc
> [   35.461301]  oom_kill_process.cold+0x9/0xe
> [   35.465390]  out_of_memory+0x1b1/0x260
> [   35.469135]  __alloc_pages_nodemask+0xe1d/0xed0
> [   35.473658]  ? alloc_page_buffers+0x81/0x130
> [   35.477923]  pagecache_get_page+0xae/0x260
> [   35.482014]  grab_cache_page_write_begin+0x1c/0x30
> [   35.486798]  block_write_begin+0x1e/0x90
> [   35.490716]  blkdev_write_begin+0x1e/0x20
> [   35.494719]  ? bdev_evict_inode+0xd0/0xd0
> [   35.498722]  generic_perform_write+0x97/0x180
> [   35.503073]  __generic_file_write_iter+0x140/0x1f0
> [   35.507857]  blkdev_write_iter+0xc0/0x190
> [   35.511860]  __vfs_write+0x132/0x1e0
> [   35.515431]  vfs_write+0xa1/0x1a0
> [   35.518742]  ksys_pwrite64+0x50/0x80
> [   35.522315]  __ia32_sys_ia32_pwrite64+0x16/0x20
> [   35.526845]  do_syscall_32_irqs_on+0x3d/0x250
> [   35.531195]  ? do_user_addr_fault+0x1a0/0x3c0
> [   35.535548]  ? __prepare_exit_to_usermode+0x50/0x1a0
> [   35.540504]  do_fast_syscall_32+0x39/0xb0
> [   35.544508]  entry_SYSENTER_32+0xa5/0xf8
> [   35.548426] EIP: 0xb7efb549
> [   35.551218] Code: 03 74 c0 01 10 05 03 74 b8 01 10 06 03 74 b4 01
> 10 07 03 74 b0 01 10 08 03 74 d8 01 00 00 00 00 00 51 52 55 89 e5 0f
> 34 cd 80 <5d> 5a 59 c3 90 90 90 90 8d 76 00 58 b8 77 00 00 00 cd 80 90
> 8d 76
> [   35.569962] EAX: ffffffda EBX: 00000003 ECX: b77ef010 EDX: 00400000
> [   35.576217] ESI: 38400000 EDI: 00000074 EBP: 07438400 ESP: bfdff180
> [   35.582476] DS: 007b ES: 007b FS: 0000 GS: 0033 SS: 007b EFLAGS: 00000246
> [   35.589260] Mem-Info:
> [   35.591552] active_anon:5403 inactive_anon:2167 isolated_anon:0
> [   35.591552]  active_file:4174 inactive_file:212518 isolated_file:0
> [   35.591552]  unevictable:0 dirty:16699 writeback:6001 unstable:0
> [   35.591552]  slab_reclaimable:5868 slab_unreclaimable:3494
> [   35.591552]  mapped:6285 shmem:2236 pagetables:176 bounce:0
> [   35.591552]  free:264050 free_pcp:1186 free_cma:0
> [   35.625311] Node 0 active_anon:21612kB inactive_anon:8668kB
> active_file:16696kB inactive_file:850072kB unevictable:0kB
> isolated(anon):0kB isolated(file):0kB mapped:25140kB dirty:62704kB
> writeback:22764kB shmem:8944kB writeback_tmp:0kB unstable:0kB
> all_unreclaimable? yes
> [   35.649169] DMA free:3360kB min:68kB low:84kB high:100kB
> reserved_highatomic:0KB active_anon:0kB inactive_anon:0kB
> active_file:0kB inactive_file:12012kB unevictable:0kB
> writepending:12012kB present:15964kB managed:15876kB mlocked:0kB
> kernel_stack:0kB pagetables:0kB bounce:0kB free_pcp:0kB local_pcp:0kB
> free_cma:0kB
> [   35.677015] lowmem_reserve[]: 0 824 1947 824
> [   35.681286] Normal free:4300kB min:7732kB low:8640kB high:9548kB
> reserved_highatomic:0KB active_anon:0kB inactive_anon:0kB
> active_file:1132kB inactive_file:786452kB unevictable:0kB
> writepending:64032kB present:884728kB managed:845292kB mlocked:0kB
> kernel_stack:1112kB pagetables:0kB bounce:0kB free_pcp:2392kB
> local_pcp:456kB free_cma:0kB
> [   35.711109] lowmem_reserve[]: 0 0 8980 0
> [   35.715051] HighMem free:1048740kB min:512kB low:1748kB high:2984kB
> reserved_highatomic:0KB active_anon:21612kB inactive_anon:8668kB
> active_file:15564kB inactive_file:51556kB unevictable:0kB
> writepending:0kB present:1149540kB managed:1149540kB mlocked:0kB
> kernel_stack:0kB pagetables:704kB bounce:0kB free_pcp:2216kB
> local_pcp:200kB free_cma:0kB
> [   35.745418] lowmem_reserve[]: 0 0 0 0
> [   35.749117] DMA: 7*4kB (UE) 1*8kB (U) 2*16kB (UE) 1*32kB (E) 1*64kB
> (E) 1*128kB (E) 0*256kB 0*512kB 1*1024kB (E) 1*2048kB (E) 0*4096kB =
> 3364kB
> [   35.762006] Normal: 19*4kB (U) 18*8kB (UE) 18*16kB (UE) 12*32kB
> (UE) 6*64kB (U) 2*128kB (U) 2*256kB (UE) 1*512kB (E) 0*1024kB 1*2048kB
> (U) 0*4096kB = 4604kB
> [   35.776020] HighMem: 1*4kB (U) 0*8kB 0*16kB 1*32kB (M) 0*64kB
> 1*128kB (M) 0*256kB 0*512kB 0*1024kB 0*2048kB 256*4096kB (M) =
> 1048740kB
> [   35.788093] Node 0 hugepages_total=0 hugepages_free=0
> hugepages_surp=0 hugepages_size=4096kB
> [   35.796533] 218903 total pagecache pages
> [   35.800503] 0 pages in swap cache
> [   35.803873] Swap cache stats: add 0, delete 0, find 0/0
> [   35.809145] Free swap  = 0kB
> [   35.812083] Total swap = 0kB
> [   35.815021] 512558 pages RAM
> [   35.817957] 287385 pages HighMem/MovableOnly
> [   35.822221] 9881 pages reserved
> [   35.825368] Tasks state (memory values in pages):
> [   35.830124] [  pid  ]   uid  tgid total_vm      rss pgtables_bytes
> swapents oom_score_adj name
> [   35.838791] [    225]     0   225     3425     1294    24576
> 0             0 systemd-journal
> [   35.847868] [    240]     0   240     3326      868    20480
> 0         -1000 systemd-udevd
> [   35.856785] [    243]   994   243     3929      450    24576
> 0             0 systemd-timesyn
> [   35.865874] [    260]   993   260     1569      786    20480
> 0             0 systemd-network
> [   35.874966] [    278]   992   278     1729      843    20480
> 0             0 systemd-resolve
> [   35.884007] [    282]     0   282      809      428    16384
> 0             0 crond
> [   35.892229] [    283]     0   283     2032     1104    20480
> 0             0 haveged
> [   35.900635] [    284]     0   284      922      194    16384
> 0             0 klogd
> [   35.908820] [    285]     0   285     5638     1481    32768
> 0             0 thermald
> [   35.917304] [    286]   995   286     1182      664    20480
> 0             0 avahi-daemon
> [   35.926133] [    287]   996   287     1174      835    24576
> 0          -900 dbus-daemon
> [   35.934880] [    288]   995   288     1182       58    20480
> 0             0 avahi-daemon
> [   35.943710] [    289]     0   289      921      409    16384
> 0             0 syslogd
> [   35.952108] [    290]     0   290     1468      998    20480
> 0             0 systemd-logind
> [   35.961060] [    303]     0   303      594       15    16384
> 0             0 acpid
> [   35.969275] [    304]     0   304    11786     2635    45056
> 0             0 NetworkManager
> [   35.978282] [    305]     0   305      677      429    16384
> 0             0 atd
> [   35.986280] [    323]     0   323     1347      321    20480
> 0             0 systemd-hostnam
> [   35.995318] [    334] 65534   334      729       32    16384
> 0             0 dnsmasq
> [   36.003708] [    335]     0   335      666      443    16384
> 0             0 agetty
> [   36.012019] [    336]     0   336      947      710    20480
> 0             0 login
> [   36.020246] [    337]     0   337      666      419    16384
> 0             0 agetty
> [   36.028555] [    348]   998   348    19521     2782    65536
> 0             0 polkitd
> [   36.036901] [    356]     0   356     1892     1183    20480
> 0             0 systemd
> [   36.045300] [    357]     0   357     2320      316    20480
> 0             0 (sd-pam)
> [   36.053731] [    361]     0   361      971      721    16384
> 0             0 sh
> [   36.061698] [    365]     0   365      920      610    16384
> 0             0 su
> [   36.069682] [    366]     0   366      971      689    16384
> 0             0 sh
> [   36.077664] [    371]     0   371      903      580    16384
> 0             0 lava-test-runne
> [   36.086761] [    381]     0   381      903      520    16384
> 0             0 lava-test-shell
> [   36.095852] [    382]     0   382      903      581    16384
> 0             0 sh
> [   36.103816] [    391]     0   391     1976     1688    24576
> 0             0 mkfs.ext4
> [   36.112336] oom-kill:constraint=CONSTRAINT_NONE,nodemask=(null),cpuset=/,mems_allowed=0,global_oom,task_memcg=/,task=polkitd,pid=348,uid=998
> [   36.125003] Out of memory: Killed process 348 (polkitd)
> total-vm:78084kB, anon-rss:2980kB, file-rss:8148kB, shmem-rss:0kB,
> UID:998 pgtables:64kB oom_score_adj:0
> [   36.139810] oom_reaper: reaped process 348 (polkitd), now
> anon-rss:0kB, file-rss:0kB, shmem-rss:0kB
> [   36.148879] mkfs.ext4 invoked oom-killer:
> gfp_mask=0x101cc0(GFP_USER|__GFP_WRITE), order=0, oom_score_adj=0
> [   36.158626] CPU: 1 PID: 391 Comm: mkfs.ext4 Not tainted
> 5.7.0-rc6-next-20200521 #1
> [   36.166220] Hardware name: Supermicro SYS-5019S-ML/X11SSH-F, BIOS
> 2.2 05/23/2018
> [   36.173604] Call Trace:
> [   36.176050]  dump_stack+0x54/0x6e
> [   36.179360]  dump_header+0x3d/0x1d2
> [   36.182844]  ? oom_badness.part.0+0x11/0x120
> [   36.187110]  ? ___ratelimit+0x8f/0xdc
> [   36.190773]  oom_kill_process.cold+0x9/0xe
> [   36.194863]  out_of_memory+0x1b1/0x260
> [   36.198610]  __alloc_pages_nodemask+0xe1d/0xed0
> [   36.203141]  ? alloc_page_buffers+0x81/0x130
> [   36.207406]  pagecache_get_page+0xae/0x260
> [   36.211496]  grab_cache_page_write_begin+0x1c/0x30
> [   36.216281]  block_write_begin+0x1e/0x90
> [   36.220197]  blkdev_write_begin+0x1e/0x20
> [   36.224201]  ? bdev_evict_inode+0xd0/0xd0
> [   36.228205]  generic_perform_write+0x97/0x180
> [   36.232557]  __generic_file_write_iter+0x140/0x1f0
> [   36.237340]  blkdev_write_iter+0xc0/0x190
> [   36.241344]  __vfs_write+0x132/0x1e0
> [   36.244915]  vfs_write+0xa1/0x1a0
> [   36.248225]  ksys_pwrite64+0x50/0x80
> [   36.251797]  __ia32_sys_ia32_pwrite64+0x16/0x20
> [   36.256319]  do_syscall_32_irqs_on+0x3d/0x250
> [   36.260693]  ? do_user_addr_fault+0x1a0/0x3c0
> [   36.265045]  ? __prepare_exit_to_usermode+0x50/0x1a0
> [   36.270004]  do_fast_syscall_32+0x39/0xb0
> [   36.274006]  entry_SYSENTER_32+0xa5/0xf8
> [   36.277926] EIP: 0xb7efb549
> [   36.280728] Code: 03 74 c0 01 10 05 03 74 b8 01 10 06 03 74 b4 01
> 10 07 03 74 b0 01 10 08 03 74 d8 01 00 00 00 00 00 51 52 55 89 e5 0f
> 34 cd 80 <5d> 5a 59 c3 90 90 90 90 8d 76 00 58 b8 77 00 00 00 cd 80 90
> 8d 76
> [   36.299471] EAX: ffffffda EBX: 00000003 ECX: b77ef010 EDX: 00400000
> [   36.305728] ESI: 38400000 EDI: 00000074 EBP: 07438400 ESP: bfdff180
> [   36.311986] DS: 007b ES: 007b FS: 0000 GS: 0033 SS: 007b EFLAGS: 00000246
> [   36.318783] Mem-Info:
> [   36.321070] active_anon:4659 inactive_anon:2167 isolated_anon:0
> [   36.321070]  active_file:4639 inactive_file:212058 isolated_file:0
> [   36.321070]  unevictable:0 dirty:14286 writeback:23 unstable:0
> [   36.321070]  slab_reclaimable:5883 slab_unreclaimable:3313
> [   36.321070]  mapped:5709 shmem:2236 pagetables:176 bounce:0
> [   36.321070]  free:264784 free_pcp:1341 free_cma:0
> [   36.354669] Node 0 active_anon:18636kB inactive_anon:8668kB
> active_file:18556kB inactive_file:848232kB unevictable:0kB
> isolated(anon):0kB isolated(file):0kB mapped:22836kB dirty:57144kB
> writeback:92kB shmem:8944kB writeback_tmp:0kB unstable:0kB
> all_unreclaimable? yes
> [   36.378296] DMA free:3364kB min:68kB low:84kB high:100kB
> reserved_highatomic:0KB active_anon:0kB inactive_anon:0kB
> active_file:0kB inactive_file:12124kB unevictable:0kB
> writepending:12132kB present:15964kB managed:15876kB mlocked:0kB
> kernel_stack:0kB pagetables:0kB bounce:0kB free_pcp:0kB local_pcp:0kB
> free_cma:0kB
> [   36.406167] lowmem_reserve[]: 0 824 1947 824
> [   36.410467] Normal free:4552kB min:7732kB low:8640kB high:9548kB
> reserved_highatomic:0KB active_anon:0kB inactive_anon:0kB
> active_file:1132kB inactive_file:786524kB unevictable:0kB
> writepending:45100kB present:884728kB managed:845292kB mlocked:0kB
> kernel_stack:1112kB pagetables:0kB bounce:0kB free_pcp:2548kB
> local_pcp:1432kB free_cma:0kB
> [   36.440330] lowmem_reserve[]: 0 0 8980 0
> [   36.444274] HighMem free:1051220kB min:512kB low:1748kB high:2984kB
> reserved_highatomic:0KB active_anon:18636kB inactive_anon:8668kB
> active_file:17424kB inactive_file:49696kB unevictable:0kB
> writepending:0kB present:1149540kB managed:1149540kB mlocked:0kB
> kernel_stack:0kB pagetables:704kB bounce:0kB free_pcp:2812kB
> local_pcp:516kB free_cma:0kB
> [   36.474680] lowmem_reserve[]: 0 0 0 0
> [   36.478401] DMA: 3*4kB (U) 1*8kB (U) 1*16kB (U) 0*32kB 2*64kB (UE)
> 1*128kB (E) 0*256kB 0*512kB 1*1024kB (E) 1*2048kB (E) 0*4096kB =
> 3364kB
> [   36.490847] Normal: 19*4kB (U) 22*8kB (UE) 19*16kB (UE) 13*32kB
> (UE) 6*64kB (U) 2*128kB (U) 2*256kB (UE) 1*512kB (E) 0*1024kB 1*2048kB
> (U) 0*4096kB = 4684kB
> [   36.504851] HighMem: 119*4kB (UM) 48*8kB (M) 12*16kB (UM) 11*32kB
> (M) 8*64kB (UM) 6*128kB (M) 0*256kB 0*512kB 0*1024kB 0*2048kB
> 256*4096kB (M) = 1051260kB
> [   36.518695] Node 0 hugepages_total=0 hugepages_free=0
> hugepages_surp=0 hugepages_size=4096kB
> [   36.527151] 218965 total pagecache pages
> [   36.531095] 0 pages in swap cache
> [   36.534430] Swap cache stats: add 0, delete 0, find 0/0
> [   36.539697] Free swap  = 0kB
> [   36.542602] Total swap = 0kB
> [   36.545531] 512558 pages RAM
> [   36.548436] 287385 pages HighMem/MovableOnly
> [   36.552729] 9881 pages reserved
> [   36.555897] Tasks state (memory values in pages):
> [   36.560621] [  pid  ]   uid  tgid total_vm      rss pgtables_bytes
> swapents oom_score_adj name
> [   36.569230] [    225]     0   225     3425     1294    28672
> 0             0 systemd-journal
> [   36.578295] [    240]     0   240     3326      868    20480
> 0         -1000 systemd-udevd
> [   36.587186] [    243]   994   243     3929      450    24576
> 0             0 systemd-timesyn
> [   36.596249] [    260]   993   260     1569      786    20480
> 0             0 systemd-network
> [   36.605307] [    278]   992   278     1729      843    20480
> 0             0 systemd-resolve
> [   36.614363] [    282]     0   282      809      428    16384
> 0             0 crond
> [   36.622551] [    283]     0   283     2032     1104    20480
> 0             0 haveged
> [   36.630918] [    284]     0   284      922      194    16384
> 0             0 klogd
> [   36.639114] [    285]     0   285     5638     1481    32768
> 0             0 thermald
> [   36.647563] [    286]   995   286     1182      664    20480
> 0             0 avahi-daemon
> [   36.656362] [    287]   996   287     1174      835    24576
> 0          -900 dbus-daemon
> [   36.665081] [    288]   995   288     1182       58    20480
> 0             0 avahi-daemon
> [   36.673884] [    289]     0   289      921      409    16384
> 0             0 syslogd
> [   36.682249] [    290]     0   290     1468      998    20480
> 0             0 systemd-logind
> [   36.691228] [    303]     0   303      594       15    16384
> 0             0 acpid
> [   36.699425] [    304]     0   304    11786     2635    45056
> 0             0 NetworkManager
> [   36.708395] [    305]     0   305      677      429    16384
> 0             0 atd
> [   36.716394] [    323]     0   323     1347      321    20480
> 0             0 systemd-hostnam
> [   36.725435] [    334] 65534   334      729       32    16384
> 0             0 dnsmasq
> [   36.733781] [    335]     0   335      666      443    16384
> 0             0 agetty
> [   36.742041] [    336]     0   336      947      710    20480
> 0             0 login
> [   36.750237] [    337]     0   337      666      419    16384
> 0             0 agetty
> [   36.758514] [    356]     0   356     1892     1183    20480
> 0             0 systemd
> [   36.766877] [    357]     0   357     2320      316    20480
> 0             0 (sd-pam)
> [   36.775326] [    361]     0   361      971      721    16384
> 0             0 sh
> [   36.783257] [    365]     0   365      920      610    16384
> 0             0 su
> [   36.791170] [    366]     0   366      971      689    16384
> 0             0 sh
> [   36.799082] [    371]     0   371      903      580    16384
> 0             0 lava-test-runne
> [   36.808122] [    381]     0   381      903      520    16384
> 0             0 lava-test-shell
> [   36.817161] [    382]     0   382      903      581    16384
> 0             0 sh
> [   36.825073] [    391]     0   391     1976     1688    24576
> 0             0 mkfs.ext4
> [   36.833591] oom-kill:constraint=CONSTRAINT_NONE,nodemask=(null),cpuset=/,mems_allowed=0,global_oom,task_memcg=/,task=NetworkManager,pid=304,uid=0
> [   36.846621] Out of memory: Killed process 304 (NetworkManager)
> total-vm:47144kB, anon-rss:1396kB, file-rss:9144kB, shmem-rss:0kB,
> UID:0 pgtables:44kB oom_score_adj:0
> [   36.861729] oom_reaper: reaped process 304 (NetworkManager), now
> anon-rss:0kB, file-rss:0kB, shmem-rss:0kB
> [   36.861738] klogd invoked oom-killer:
> gfp_mask=0xc2cc0(GFP_KERNEL|__GFP_NOWARN|__GFP_COMP|__GFP_NOMEMALLOC),
> order=0, oom_score_adj=0
> [   36.883368] CPU: 2 PID: 284 Comm: klogd Not tainted
> 5.7.0-rc6-next-20200521 #1
> [   36.890607] Hardware name: Supermicro SYS-5019S-ML/X11SSH-F, BIOS
> 2.2 05/23/2018
> [   36.897992] Call Trace:
> [   36.900438]  dump_stack+0x54/0x6e
> [   36.903763]  dump_header+0x3d/0x1d2
> [   36.907247]  ? oom_badness.part.0+0x11/0x120
> [   36.911510]  ? ___ratelimit+0x8f/0xdc
> [   36.915167]  oom_kill_process.cold+0x9/0xe
> [   36.919258]  out_of_memory+0x1b1/0x260
> [   36.923005]  __alloc_pages_nodemask+0xe1d/0xed0
> [   36.927537]  alloc_slab_page+0x13d/0x2c0
> [   36.931453]  new_slab+0x22e/0x280
> [   36.934766]  ? cpumask_next_and+0x18/0x20
> [   36.938777]  ___slab_alloc.constprop.0+0x248/0x4a0
> [   36.943563]  ? __alloc_skb+0x64/0x1a0
> [   36.947228]  ? __alloc_skb+0x41/0x1a0
> [   36.950885]  __slab_alloc.constprop.0+0xf/0x20
> [   36.955321]  ? __slab_alloc.constprop.0+0xf/0x20
> [   36.959932]  __kmalloc_track_caller+0x23e/0x270
> [   36.964456]  ? __alloc_skb+0x64/0x1a0
> [   36.968114]  ? _cond_resched+0x12/0x30
> [   36.971857]  __kmalloc_reserve.isra.0+0x1d/0x70
> [   36.976380]  __alloc_skb+0x64/0x1a0
> [   36.979866]  ? update_rq_clock.part.0+0x16/0xe0
> [   36.984389]  alloc_skb_with_frags+0x3b/0x1a0
> [   36.988665]  sock_alloc_send_pskb+0x1c7/0x1f0
> [   36.993040]  ? selinux_inet_conn_established+0x40/0x40
> [   36.998179]  unix_dgram_sendmsg+0x12a/0x690
> [   37.002365]  ? selinux_socket_recvmsg+0x20/0x20
> [   37.006897]  ? unix_dgram_connect+0x2f0/0x2f0
> [   37.011247]  sock_sendmsg+0x5c/0x60
> [   37.014730]  __sys_sendto+0xe1/0x120
> [   37.018301]  ? msg_print_text+0x80/0x1c0
> [   37.022219]  ? do_syslog+0x19c/0x940
> [   37.025788]  ? do_syslog+0x878/0x940
> [   37.029358]  ? do_syslog+0x878/0x940
> [   37.032931]  ? kunmap_atomic_high+0x4e/0x58
> [   37.037109]  ? handle_mm_fault+0x25c/0xc60
> [   37.041209]  __ia32_sys_socketcall+0x29f/0x330
> [   37.045665]  do_syscall_32_irqs_on+0x3d/0x250
> [   37.050038]  ? do_user_addr_fault+0x1a0/0x3c0
> [   37.054388]  ? __prepare_exit_to_usermode+0x50/0x1a0
> [   37.059346]  do_fast_syscall_32+0x39/0xb0
> [   37.063351]  entry_SYSENTER_32+0xa5/0xf8
> [   37.067276] EIP: 0xb7f66549
>
> ref:
> https://lkft.validation.linaro.org/scheduler/job/1444120#L1220
>
> --
> Linaro LKFT
> https://lkft.linaro.org



-- 
Thanks
Yafang

Re: [PATCH v3 2/2] mm, memcg: Decouple e{low,min} state mutations from protection checks

[Naresh Kamboju]

On Fri, 22 May 2020 at 17:49, Yafang Shao <laoar.shao@gmail.com> wrote:
>
> On Fri, May 22, 2020 at 7:01 PM Naresh Kamboju
> <naresh.kamboju@linaro.org> wrote:
> >
> > On Tue, 5 May 2020 at 14:12, Yafang Shao <laoar.shao@gmail.com> wrote:
> > >
> > > From: Chris Down <chris@chrisdown.name>
> > >
> > > mem_cgroup_protected currently is both used to set effective low and min
> > > and return a mem_cgroup_protection based on the result.  As a user, this
> > > can be a little unexpected: it appears to be a simple predicate function,
> > > if not for the big warning in the comment above about the order in which
> > > it must be executed.
> > >
> > > This change makes it so that we separate the state mutations from the
> > > actual protection checks, which makes it more obvious where we need to be
> > > careful mutating internal state, and where we are simply checking and
> > > don't need to worry about that.
> >
> > This patch is causing oom-killer while running mkfs -t ext4 on i386 kernel
> > running on x86_64 machine version linux-next 5.7.0-rc6-next-20200521.
> >
>
> Hi Narash,
>
> Thanks for your report.
> My suggestion to the issue found by you is reverting this bad commit.

Thanks for giving details on this problem.
I am not sure who will propose reverting this patch on the linux-next tree.
Please add Reported-by if it is sane.

>
> As I have explained earlier in another mail thread [1] that the usage
> around memcg->{emin, elow} is very buggy.
> We shouldn't use memcg->{emin, elow} in the reclaim context directly,
> because  these two values can be modified by many reclaimers, so the
> good usage of it is storing the protection value into the
> scan_control. IOW, different reclaimers have different protection.
> But unfortunately my suggestion is ignored.
>
> We can set them to 0 before using them to workaround the issue found
> by you, but the fact is that we will introduce a new issue once we fix
> an old issue.
>
> [1]. https://lore.kernel.org/linux-mm/20200425152418.28388-1-laoar.shao@gmail.com/


- Naresh

Re: [PATCH v3 2/2] mm, memcg: Decouple e{low,min} state mutations from protection checks

[Yafang Shao]

On Fri, May 22, 2020 at 11:52 PM Naresh Kamboju
<naresh.kamboju@linaro.org> wrote:
>
> On Fri, 22 May 2020 at 17:49, Yafang Shao <laoar.shao@gmail.com> wrote:
> >
> > On Fri, May 22, 2020 at 7:01 PM Naresh Kamboju
> > <naresh.kamboju@linaro.org> wrote:
> > >
> > > On Tue, 5 May 2020 at 14:12, Yafang Shao <laoar.shao@gmail.com> wrote:
> > > >
> > > > From: Chris Down <chris@chrisdown.name>
> > > >
> > > > mem_cgroup_protected currently is both used to set effective low and min
> > > > and return a mem_cgroup_protection based on the result.  As a user, this
> > > > can be a little unexpected: it appears to be a simple predicate function,
> > > > if not for the big warning in the comment above about the order in which
> > > > it must be executed.
> > > >
> > > > This change makes it so that we separate the state mutations from the
> > > > actual protection checks, which makes it more obvious where we need to be
> > > > careful mutating internal state, and where we are simply checking and
> > > > don't need to worry about that.
> > >
> > > This patch is causing oom-killer while running mkfs -t ext4 on i386 kernel
> > > running on x86_64 machine version linux-next 5.7.0-rc6-next-20200521.
> > >
> >
> > Hi Narash,
> >
> > Thanks for your report.
> > My suggestion to the issue found by you is reverting this bad commit.
>
> Thanks for giving details on this problem.
> I am not sure who will propose reverting this patch on the linux-next tree.
> Please add Reported-by if it is sane.
>

I will do it.
If no one has objection to my proposal, I will send it tomorrow.

> >
> > As I have explained earlier in another mail thread [1] that the usage
> > around memcg->{emin, elow} is very buggy.
> > We shouldn't use memcg->{emin, elow} in the reclaim context directly,
> > because  these two values can be modified by many reclaimers, so the
> > good usage of it is storing the protection value into the
> > scan_control. IOW, different reclaimers have different protection.
> > But unfortunately my suggestion is ignored.
> >
> > We can set them to 0 before using them to workaround the issue found
> > by you, but the fact is that we will introduce a new issue once we fix
> > an old issue.
> >
> > [1]. https://lore.kernel.org/linux-mm/20200425152418.28388-1-laoar.shao@gmail.com/
>
>
> - Naresh



-- 
Thanks
Yafang

Re: [PATCH v3 2/2] mm, memcg: Decouple e{low,min} state mutations from protection checks

[Chris Down]

Yafang Shao writes:
>I will do it.
>If no one has objection to my proposal, I will send it tomorrow.

If the fixup patch works, just send that. Otherwise, sure.

Re: [PATCH v3 2/2] mm, memcg: Decouple e{low,min} state mutations from protection checks

[Chris Down]

Chris Down writes:
>Yafang Shao writes:
>>I will do it.
>>If no one has objection to my proposal, I will send it tomorrow.
>
>If the fixup patch works, just send that. Otherwise, sure.

Oh, I see the other reply from Naresh now saying it didn't help.

Sure, feel free to do that for now then while we work out what the real problem 
is.

Re: [PATCH v3 2/2] mm, memcg: Decouple e{low,min} state mutations from protection checks

[Yafang Shao]

On Sat, May 23, 2020 at 12:07 AM Chris Down <chris@chrisdown.name> wrote:
>
> Chris Down writes:
> >Yafang Shao writes:
> >>I will do it.
> >>If no one has objection to my proposal, I will send it tomorrow.
> >
> >If the fixup patch works, just send that. Otherwise, sure.
>
> Oh, I see the other reply from Naresh now saying it didn't help.
>
> Sure, feel free to do that for now then while we work out what the real problem
> is.

Regarding the root cause, my guess is it makes a similar mistake that
I tried to fix in the previous patch that the direct reclaimer read a
stale protection value.  But I don't think it is worth to add another
fix. The best way is to revert this commit.

-- 
Thanks
Yafang