Patch "mm: page_alloc: __GFP_NOWARN shouldn't suppress stall warnings"
changed to drop __GFP_NOWARN when calling warn_alloc() for stall warning.
Although I suggested for two times to drop __GFP_NOWARN when warn_alloc()
for stall warning was proposed, Michal Hocko does not want to print stall
warnings when __GFP_NOWARN is given [1][2].
"I am not going to allow defining a weird __GFP_NOWARN semantic which
allows warnings but only sometimes. At least not without having a proper
way to silence both failures _and_ stalls or just stalls. I do not
really thing this is worth the additional gfp flag."
I don't know whether he is aware of "mm: page_alloc: __GFP_NOWARN
shouldn't suppress stall warnings" patch, but I assume that
no response means he finally accepted this change. Therefore,
this patch splits into a function for reporting allocation stalls
and a function for reporting allocation failures, due to below reasons.
(1) Dropping __GFP_NOWARN when calling warn_alloc() causes
"mode:%#x(%pGg)" to report incorrect flags. It can confuse
developers when scanning the source code for corresponding
location.
(2) Not reporting when debug_guardpage_minorder() > 0 causes failing
to report stall warnings. Stall warnings should not be be disabled
by debug_guardpage_minorder() > 0 as well as __GFP_NOWARN.
(3) Sharing warn_alloc() for reporting stalls (which is guaranteed
to be schedulable context) and for reporting failures (which is
not guaranteed to be schedulable context) is inconvenient when
adding a mutex for serializing printk() messages and/or filtering
events which should be handled for further analysis based on
function name.
# stap -F -g -e 'probe kernel.function("warn_alloc").return {
if (determine_whether_reason_is_allocation_stall)
panic("MemAlloc stall detected."); }'
# stap -F -g -e 'probe kernel.function("warn_alloc_stall").return {
panic("MemAlloc stall detected."); }'
Although adding allocation watchdog [3] will do it more powerfully,
allocation watchdog discussion is still stalling. Thus, for now
I propose triggering from warn_alloc_stall().
[1] http://lkml.kernel.org/r/20160929091040.GE408@xxxxxxxxxxxxxx
[2] http://lkml.kernel.org/r/20170114090613.GD9962@xxxxxxxxxxxxxx
[3] http://lkml.kernel.org/r/1489578541-81526-1-git-send-email-penguin-kernel@xxxxxxxxxxxxxxxxxxx
Signed-off-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxxxx>
---
mm/page_alloc.c | 41 ++++++++++++++++++++++++++---------------
1 file changed, 26 insertions(+), 15 deletions(-)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 32b31d6..bde435d 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3124,11 +3124,20 @@ static inline bool should_suppress_show_mem(void)
return ret;
}
-static void warn_alloc_show_mem(gfp_t gfp_mask, nodemask_t *nodemask)
+static void warn_alloc_common(gfp_t gfp_mask, nodemask_t *nodemask)
{
unsigned int filter = SHOW_MEM_FILTER_NODES;
static DEFINE_RATELIMIT_STATE(show_mem_rs, HZ, 1);
+ pr_cont(", mode:%#x(%pGg), nodemask=", gfp_mask, &gfp_mask);
+ if (nodemask)
+ pr_cont("%*pbl\n", nodemask_pr_args(nodemask));
+ else
+ pr_cont("(null)\n");
+
+ cpuset_print_current_mems_allowed();
+
+ dump_stack();
if (should_suppress_show_mem() || !__ratelimit(&show_mem_rs))
return;
@@ -3147,6 +3156,20 @@ static void warn_alloc_show_mem(gfp_t gfp_mask, nodemask_t *nodemask)
show_mem(filter, nodemask);
}
+static void warn_alloc_stall(gfp_t gfp_mask, nodemask_t *nodemask,
+ unsigned long alloc_start, int order)
+{
+ static DEFINE_RATELIMIT_STATE(stall_rs, DEFAULT_RATELIMIT_INTERVAL,
+ DEFAULT_RATELIMIT_BURST);
+
+ if (!__ratelimit(&stall_rs))
+ return;
+
+ pr_warn("%s: page allocation stalls for %ums, order:%u",
+ current->comm, jiffies_to_msecs(jiffies-alloc_start), order);
+ warn_alloc_common(gfp_mask, nodemask);
+}
+
void warn_alloc(gfp_t gfp_mask, nodemask_t *nodemask, const char *fmt, ...)
{
struct va_format vaf;
@@ -3165,17 +3188,7 @@ void warn_alloc(gfp_t gfp_mask, nodemask_t *nodemask, const char *fmt, ...)
vaf.va = &args;
pr_cont("%pV", &vaf);
va_end(args);
-
- pr_cont(", mode:%#x(%pGg), nodemask=", gfp_mask, &gfp_mask);
- if (nodemask)
- pr_cont("%*pbl\n", nodemask_pr_args(nodemask));
- else
- pr_cont("(null)\n");
-
- cpuset_print_current_mems_allowed();
-
- dump_stack();
- warn_alloc_show_mem(gfp_mask, nodemask);
+ warn_alloc_common(gfp_mask, nodemask);
}
static inline struct page *
@@ -3814,9 +3827,7 @@ bool gfp_pfmemalloc_allowed(gfp_t gfp_mask)
/* Make sure we know about allocations which stall for too long */
if (time_after(jiffies, alloc_start + stall_timeout)) {
- warn_alloc(gfp_mask & ~__GFP_NOWARN, ac->nodemask,
- "page allocation stalls for %ums, order:%u",
- jiffies_to_msecs(jiffies-alloc_start), order);
+ warn_alloc_stall(gfp_mask, ac->nodemask, alloc_start, order);
stall_timeout += 10 * HZ;
}
--
1.8.3.1
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@xxxxxxxxx. For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
