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SubjectRe: [PATCH 2/2] mm, oom: do not enfore OOM killer for __GFP_NOFAIL automatically
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Tetsuo Handa wrote:
> Michal Hocko wrote:
> > On Thu 08-12-16 21:53:44, Tetsuo Handa wrote:
> > > If we could agree
> > > with calling __alloc_pages_nowmark() before out_of_memory() if __GFP_NOFAIL
> > > is given, we can avoid locking up while minimizing possibility of invoking
> > > the OOM killer...
> >
> > I do not understand. We do __alloc_pages_nowmark even when oom is called
> > for GFP_NOFAIL.
>
> Where is that? I can find __alloc_pages_nowmark() after out_of_memory()
> if __GFP_NOFAIL is given, but I can't find __alloc_pages_nowmark() before
> out_of_memory() if __GFP_NOFAIL is given.
>
> What I mean is below patch folded into
> "[PATCH 1/2] mm: consolidate GFP_NOFAIL checks in the allocator slowpath".
>
Oops, I wrongly implemented "__alloc_pages_nowmark() before out_of_memory() if
__GFP_NOFAIL is given." case. Updated version is shown below.

--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3116,23 +3116,27 @@ void warn_alloc(gfp_t gfp_mask, const char *fmt, ...)
/* The OOM killer may not free memory on a specific node */
if (gfp_mask & __GFP_THISNODE)
goto out;
+ } else {
+ /*
+ * Help non-failing allocations by giving them access to memory
+ * reserves
+ */
+ page = get_page_from_freelist(gfp_mask, order,
+ ALLOC_NO_WATERMARKS|ALLOC_CPUSET, ac);
+ /*
+ * fallback to ignore cpuset restriction if our nodes
+ * are depleted
+ */
+ if (!page)
+ page = get_page_from_freelist(gfp_mask, order,
+ ALLOC_NO_WATERMARKS, ac);
+ if (page)
+ goto out;
}
+
/* Exhausted what can be done so it's blamo time */
- if (out_of_memory(&oc) || WARN_ON_ONCE(gfp_mask & __GFP_NOFAIL)) {
+ if (out_of_memory(&oc))
*did_some_progress = 1;
-
- if (gfp_mask & __GFP_NOFAIL) {
- page = get_page_from_freelist(gfp_mask, order,
- ALLOC_NO_WATERMARKS|ALLOC_CPUSET, ac);
- /*
- * fallback to ignore cpuset restriction if our nodes
- * are depleted
- */
- if (!page)
- page = get_page_from_freelist(gfp_mask, order,
- ALLOC_NO_WATERMARKS, ac);
- }
- }
out:
mutex_unlock(&oom_lock);
return page;
@@ -3738,6 +3742,11 @@ bool gfp_pfmemalloc_allowed(gfp_t gfp_mask)
*/
WARN_ON_ONCE(order > PAGE_ALLOC_COSTLY_ORDER);

+ /* Try memory reserves and then start killing things. */
+ page = __alloc_pages_may_oom(gfp_mask, order, ac, &did_some_progress);
+ if (page)
+ goto got_pg;
+
cond_resched();
goto retry;
}
I'm calling __alloc_pages_may_oom() from nopage: because we reach without
calling __alloc_pages_may_oom(), for PATCH 1/2 is not for stop enforcing
the OOM killer for __GFP_NOFAIL.

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