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SubjectRe: [PATCH] Add slowpath enter/exit trace events
On Thu 23-11-17 11:43:36, peter.enderborg@sony.com wrote:
> From: Peter Enderborg <peter.enderborg@sony.com>
>
> The warning of slow allocation has been removed, this is
> a other way to fetch that information. But you need
> to enable the trace. The exit function also returns
> information about the number of retries, how long
> it was stalled and failure reason if that happened.

I think this is just too excessive. We already have a tracepoint for the
allocation exit. All we need is an entry to have a base to compare with.
Another usecase would be to measure allocation latency. Information you
are adding can be (partially) covered by existing tracepoints.

> Signed-off-by: Peter Enderborg <peter.enderborg@sony.com>
> ---
> include/trace/events/kmem.h | 68 +++++++++++++++++++++++++++++++++++++++++++++
> mm/page_alloc.c | 62 +++++++++++++++++++++++++++++++----------
> 2 files changed, 116 insertions(+), 14 deletions(-)
>
> diff --git a/include/trace/events/kmem.h b/include/trace/events/kmem.h
> index eb57e30..bb882ca 100644
> --- a/include/trace/events/kmem.h
> +++ b/include/trace/events/kmem.h
> @@ -315,6 +315,74 @@ TRACE_EVENT(mm_page_alloc_extfrag,
> __entry->change_ownership)
> );
>
> +TRACE_EVENT(mm_page_alloc_slowpath_enter,
> +
> + TP_PROTO(int alloc_order,
> + nodemask_t *nodemask,
> + gfp_t gfp_flags),
> +
> + TP_ARGS(alloc_order, nodemask, gfp_flags),
> +
> + TP_STRUCT__entry(
> + __field(int, alloc_order)
> + __field(nodemask_t *, nodemask)
> + __field(gfp_t, gfp_flags)
> + ),
> +
> + TP_fast_assign(
> + __entry->alloc_order = alloc_order;
> + __entry->nodemask = nodemask;
> + __entry->gfp_flags = gfp_flags;
> + ),
> +
> + TP_printk("alloc_order=%d nodemask=%*pbl gfp_flags=%s",
> + __entry->alloc_order,
> + nodemask_pr_args(__entry->nodemask),
> + show_gfp_flags(__entry->gfp_flags))
> +);
> +
> +TRACE_EVENT(mm_page_alloc_slowpath_exit,
> +
> + TP_PROTO(struct page *page,
> + int alloc_order,
> + nodemask_t *nodemask,
> + u64 alloc_start,
> + gfp_t gfp_flags,
> + int retrys,
> + int exit),
> +
> + TP_ARGS(page, alloc_order, nodemask, alloc_start, gfp_flags,
> + retrys, exit),
> +
> + TP_STRUCT__entry(__field(struct page *, page)
> + __field(int, alloc_order)
> + __field(nodemask_t *, nodemask)
> + __field(u64, msdelay)
> + __field(gfp_t, gfp_flags)
> + __field(int, retrys)
> + __field(int, exit)
> + ),
> +
> + TP_fast_assign(
> + __entry->page = page;
> + __entry->alloc_order = alloc_order;
> + __entry->nodemask = nodemask;
> + __entry->msdelay = jiffies_to_msecs(jiffies-alloc_start);
> + __entry->gfp_flags = gfp_flags;
> + __entry->retrys = retrys;
> + __entry->exit = exit;
> + ),
> +
> + TP_printk("page=%p alloc_order=%d nodemask=%*pbl msdelay=%llu gfp_flags=%s retrys=%d exit=%d",
> + __entry->page,
> + __entry->alloc_order,
> + nodemask_pr_args(__entry->nodemask),
> + __entry->msdelay,
> + show_gfp_flags(__entry->gfp_flags),
> + __entry->retrys,
> + __entry->exit)
> +);
> +
> #endif /* _TRACE_KMEM_H */
>
> /* This part must be outside protection */
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 48b5b01..bae9cb9 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -104,6 +104,17 @@ DEFINE_PER_CPU(struct work_struct, pcpu_drain);
> volatile unsigned long latent_entropy __latent_entropy;
> EXPORT_SYMBOL(latent_entropy);
> #endif
> +enum slowpath_exit {
> + SLOWPATH_NOZONE = -16,
> + SLOWPATH_COMPACT_DEFERRED,
> + SLOWPATH_CAN_NOT_DIRECT_RECLAIM,
> + SLOWPATH_RECURSION,
> + SLOWPATH_NO_RETRY,
> + SLOWPATH_COSTLY_ORDER,
> + SLOWPATH_OOM_VICTIM,
> + SLOWPATH_NO_DIRECT_RECLAIM,
> + SLOWPATH_ORDER
> +};
>
> /*
> * Array of node states.
> @@ -3908,8 +3919,15 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
> enum compact_result compact_result;
> int compaction_retries;
> int no_progress_loops;
> + unsigned long alloc_start = jiffies;
> unsigned int cpuset_mems_cookie;
> int reserve_flags;
> + enum slowpath_exit slowpath_exit;
> + int retry_count = 0;
> +
> + trace_mm_page_alloc_slowpath_enter(order,
> + ac->nodemask,
> + gfp_mask);
>
> /*
> * In the slowpath, we sanity check order to avoid ever trying to
> @@ -3919,7 +3937,8 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
> */
> if (order >= MAX_ORDER) {
> WARN_ON_ONCE(!(gfp_mask & __GFP_NOWARN));
> - return NULL;
> + slowpath_exit = SLOWPATH_ORDER;
> + goto fail;
> }
>
> /*
> @@ -3951,8 +3970,10 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
> */
> ac->preferred_zoneref = first_zones_zonelist(ac->zonelist,
> ac->high_zoneidx, ac->nodemask);
> - if (!ac->preferred_zoneref->zone)
> + if (!ac->preferred_zoneref->zone) {
> + slowpath_exit = SLOWPATH_NOZONE;
> goto nopage;
> + }
>
> if (gfp_mask & __GFP_KSWAPD_RECLAIM)
> wake_all_kswapds(order, ac);
> @@ -3998,8 +4019,10 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
> * system, so we fail the allocation instead of entering
> * direct reclaim.
> */
> - if (compact_result == COMPACT_DEFERRED)
> + if (compact_result == COMPACT_DEFERRED) {
> + slowpath_exit = SLOWPATH_COMPACT_DEFERRED;
> goto nopage;
> + }
>
> /*
> * Looks like reclaim/compaction is worth trying, but
> @@ -4011,6 +4034,7 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
> }
>
> retry:
> + retry_count++;
> /* Ensure kswapd doesn't accidentally go to sleep as long as we loop */
> if (gfp_mask & __GFP_KSWAPD_RECLAIM)
> wake_all_kswapds(order, ac);
> @@ -4036,13 +4060,16 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
> goto got_pg;
>
> /* Caller is not willing to reclaim, we can't balance anything */
> - if (!can_direct_reclaim)
> + if (!can_direct_reclaim) {
> + slowpath_exit = SLOWPATH_CAN_NOT_DIRECT_RECLAIM;
> goto nopage;
> + }
>
> /* Avoid recursion of direct reclaim */
> - if (current->flags & PF_MEMALLOC)
> + if (current->flags & PF_MEMALLOC) {
> + slowpath_exit = SLOWPATH_RECURSION;
> goto nopage;
> -
> + }
> /* Try direct reclaim and then allocating */
> page = __alloc_pages_direct_reclaim(gfp_mask, order, alloc_flags, ac,
> &did_some_progress);
> @@ -4056,16 +4083,18 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
> goto got_pg;
>
> /* Do not loop if specifically requested */
> - if (gfp_mask & __GFP_NORETRY)
> + if (gfp_mask & __GFP_NORETRY) {
> + slowpath_exit = SLOWPATH_NO_RETRY;
> goto nopage;
> -
> + }
> /*
> * Do not retry costly high order allocations unless they are
> * __GFP_RETRY_MAYFAIL
> */
> - if (costly_order && !(gfp_mask & __GFP_RETRY_MAYFAIL))
> + if (costly_order && !(gfp_mask & __GFP_RETRY_MAYFAIL)) {
> + slowpath_exit = SLOWPATH_COSTLY_ORDER;
> goto nopage;
> -
> + }
> if (should_reclaim_retry(gfp_mask, order, ac, alloc_flags,
> did_some_progress > 0, &no_progress_loops))
> goto retry;
> @@ -4095,9 +4124,10 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
> /* Avoid allocations with no watermarks from looping endlessly */
> if (tsk_is_oom_victim(current) &&
> (alloc_flags == ALLOC_OOM ||
> - (gfp_mask & __GFP_NOMEMALLOC)))
> + (gfp_mask & __GFP_NOMEMALLOC))) {
> + slowpath_exit = SLOWPATH_OOM_VICTIM;
> goto nopage;
> -
> + }
> /* Retry as long as the OOM killer is making progress */
> if (did_some_progress) {
> no_progress_loops = 0;
> @@ -4118,9 +4148,10 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
> * All existing users of the __GFP_NOFAIL are blockable, so warn
> * of any new users that actually require GFP_NOWAIT
> */
> - if (WARN_ON_ONCE(!can_direct_reclaim))
> + if (WARN_ON_ONCE(!can_direct_reclaim)) {
> + slowpath_exit = SLOWPATH_NO_DIRECT_RECLAIM;
> goto fail;
> -
> + }
> /*
> * PF_MEMALLOC request from this context is rather bizarre
> * because we cannot reclaim anything and only can loop waiting
> @@ -4153,6 +4184,9 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
> warn_alloc(gfp_mask, ac->nodemask,
> "page allocation failure: order:%u", order);
> got_pg:
> + trace_mm_page_alloc_slowpath_exit(page, order, ac->nodemask,
> + alloc_start, gfp_mask, retry_count, slowpath_exit);
> +
> return page;
> }
>
> --
> 2.7.4
>
> --
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--
Michal Hocko
SUSE Labs

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