Re: [patch] mm, page_alloc: reintroduce page allocation stall warning

[Michal Hocko <mhocko@suse.com>]

On Sun 29-03-26 18:08:52, David Rientjes wrote:
> Previously, we had warnings when a single page allocation took longer
> than reasonably expected.  This was introduced in commit 63f53dea0c98
> ("mm: warn about allocations which stall for too long").
> 
> The warning was subsequently reverted in commit 400e22499dd9 ("mm: don't
> warn about allocations which stall for too long") but for reasons
> unrelated to the warning itself.

I think it makes sense to summarize reasons for the revert. I would
propose to change the above to somehting like
"
The warning was subsequently reverted in commit 400e22499dd9 ("mm: don't
warn about allocations which stall for too long") because it was
possible to generate memory pressure that would effectivelly stall
further progress through printk execution.
"
 
> @@ -4841,6 +4884,9 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
>  	if (current->flags & PF_MEMALLOC)
>  		goto nopage;
>  
> +	/* If allocation has taken excessively long, warn about it */
> +	check_alloc_stall_warn(gfp_mask, ac->nodemask, order, alloc_start_time);
> +
>  	/* Try direct reclaim and then allocating */
>  	if (!compact_first) {
>  		page = __alloc_pages_direct_reclaim(gfp_mask, order, alloc_flags,

Is there any specific reason for this placement? Compaction can take
quite some time as well.

-- 
Michal Hocko
SUSE Labs