From: Michal Hocko <mhocko@xxxxxxxx>
Now that __GFP_NOFAIL doesn't override decisions to skip the oom killer
we are left with requests which require to loop inside the allocator
without invoking the oom killer (e.g. GFP_NOFS|__GFP_NOFAIL used by fs
code) and so they might, in very unlikely situations, loop for ever -
e.g. other parallel request could starve them.
This patch tries to limit the likelihood of such a lockup by giving
these __GFP_NOFAIL requests a chance to move on by consuming a small
part of memory reserves. We are using ALLOC_HARDER which should be
enough to prevent from the starvation by regular allocation requests,
yet it shouldn't consume enough from the reserves to disrupt high
priority requests (ALLOC_HIGH).
While we are at it, let's introduce a helper __alloc_pages_cpuset_fallback
which enforces the cpusets but allows to fallback to ignore them if
the first attempt fails. __GFP_NOFAIL requests can be considered
important enough to allow cpuset runaway in order for the system to move
on. It is highly unlikely that any of these will be GFP_USER anyway.
Signed-off-by: Michal Hocko <mhocko@xxxxxxxx>
---
mm/page_alloc.c | 46 ++++++++++++++++++++++++++++++++++++----------
1 file changed, 36 insertions(+), 10 deletions(-)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 2dda7c3eba52..e8e551015d48 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3064,6 +3064,26 @@ void warn_alloc(gfp_t gfp_mask, const char *fmt, ...)
}
static inline struct page *
+__alloc_pages_cpuset_fallback(gfp_t gfp_mask, unsigned int order,
+ unsigned int alloc_flags,
+ const struct alloc_context *ac)
+{
+ struct page *page;
+
+ page = get_page_from_freelist(gfp_mask, order,
+ alloc_flags|ALLOC_CPUSET, ac);
+ /*
+ * fallback to ignore cpuset restriction if our nodes
+ * are depleted
+ */
+ if (!page)
+ page = get_page_from_freelist(gfp_mask, order,
+ alloc_flags, ac);
+
+ return page;
+}
+
+static inline struct page *
__alloc_pages_may_oom(gfp_t gfp_mask, unsigned int order,
const struct alloc_context *ac, unsigned long *did_some_progress)
{
@@ -3127,17 +3147,13 @@ __alloc_pages_may_oom(gfp_t gfp_mask, unsigned int order,
if (out_of_memory(&oc) || WARN_ON_ONCE(gfp_mask & __GFP_NOFAIL)) {
*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,
+ /*
+ * Help non-failing allocations by giving them access to memory
+ * reserves
+ */
+ if (gfp_mask & __GFP_NOFAIL)
+ page = __alloc_pages_cpuset_fallback(gfp_mask, order,
ALLOC_NO_WATERMARKS, ac);
- }
}
out:
mutex_unlock(&oom_lock);
@@ -3743,6 +3759,16 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
*/
WARN_ON_ONCE(order > PAGE_ALLOC_COSTLY_ORDER);
+ /*
+ * Help non-failing allocations by giving them access to memory
+ * reserves but do not use ALLOC_NO_WATERMARKS because this
+ * could deplete whole memory reserves which would just make
+ * the situation worse
+ */
+ page = __alloc_pages_cpuset_fallback(gfp_mask, order, ALLOC_HARDER, ac);
+ if (page)
+ goto got_pg;
+
cond_resched();
goto retry;
}
--
2.10.2
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