Re: How to handle TIF_MEMDIE stalls?

Tetsuo Handa
2015-02-17T13:22:49Z

Tetsuo Handa wrote:
> Johannes Weiner wrote:
> > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > index 8e20f9c2fa5a..f77c58ebbcfa 100644
> > --- a/mm/page_alloc.c
> > +++ b/mm/page_alloc.c
> > @@ -2382,8 +2382,15 @@ __alloc_pages_may_oom(gfp_t gfp_mask, unsigned int order,
> > if (high_zoneidx < ZONE_NORMAL)
> > goto out;
> > /* The OOM killer does not compensate for light reclaim */
> > - if (!(gfp_mask & __GFP_FS))
> > + if (!(gfp_mask & __GFP_FS)) {
> > + /*
> > + * XXX: Page reclaim didn't yield anything,
> > + * and the OOM killer can't be invoked, but
> > + * keep looping as per should_alloc_retry().
> > + */
> > + *did_some_progress = 1;
> > goto out;
> > + }
>
> Why do you omit out_of_memory() call for GFP_NOIO / GFP_NOFS allocations?

I can see "possible memory allocation deadlock in %s (mode:0x%x)" warnings
at kmem_alloc() in fs/xfs/kmem.c . I think commit 9879de7373fcfb46 "mm:
page_alloc: embed OOM killing naturally into allocation slowpath" introduced
a regression and below one is the fix.

--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -2381,9 +2381,6 @@ __alloc_pages_may_oom(gfp_t gfp_mask, unsigned int order,
/* The OOM killer does not needlessly kill tasks for lowmem */
if (high_zoneidx < ZONE_NORMAL)
goto out;
- /* The OOM killer does not compensate for light reclaim */
- if (!(gfp_mask & __GFP_FS))
- goto out;
/*
* GFP_THISNODE contains __GFP_NORETRY and we never hit this.
* Sanity check for bare calls of __GFP_THISNODE, not real OOM.

BTW, I think commit c32b3cbe0d067a9c "oom, PM: make OOM detection in the freezer
path raceless" opened a race window for __alloc_pages_may_oom(__GFP_NOFAIL)
allocation to fail when OOM killer is disabled. I think something like

--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -789,7 +789,7 @@ bool out_of_memory(struct zonelist *zonelist, gfp_t gfp_mask,
bool ret = false;

down_read(&oom_sem);
- if (!oom_killer_disabled) {
+ if (!oom_killer_disabled || (gfp_mask & __GFP_NOFAIL)) {
__out_of_memory(zonelist, gfp_mask, order, nodemask, force_kill);
ret = true;
}

is needed. But such change can race with up_write() and wait_event() in
oom_killer_disable(). While the comment of oom_killer_disable() says
"The function cannot be called when there are runnable user tasks because
the userspace would see unexpected allocation failures as a result.",
aren't there still kernel threads which might do __GFP_NOFAIL allocations?