> > > Patch 4/4: We will move the order > 1 check from the current fast path
> > > to the slow path and extend
> > > the check of gfp_direct_reclaim flag also in the slow path.
> >
> > OK, let's have that go in now as well.
Hi Michal and Vlastimil,
Could you please review the changes below before I send v4 for patch 4/4?
1. We should consolidate all warnings in one place. Currently, the order > 1 warning is
in the hotpath, while others are in less likely scenarios. Moving all warnings to the
slowpath will reduce the overhead for order > 1 and increase the visibility of other
warnings.
2. We currently have two warnings for order: one for order > 1 in the hotpath and another
for order > costly_order in the laziest path. I suggest standardizing on order > 1 since
it’s been in use for a long time.
3.I don't think we need to check for __GFP_NOWARN in this case. __GFP_NOWARN is
meant to suppress allocation failure reports, but here we're dealing with bug detection, not
allocation failures.
So I'd rather use WARN_ON_ONCE than WARN_ON_ONCE_GFP.
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index c81ee5662cc7..0d3dd679d0ab 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3033,12 +3033,6 @@ struct page *rmqueue(struct zone *preferred_zone,
{
struct page *page;
- /*
- * We most definitely don't want callers attempting to
- * allocate greater than order-1 page units with __GFP_NOFAIL.
- */
- WARN_ON_ONCE((gfp_flags & __GFP_NOFAIL) && (order > 1));
-
if (likely(pcp_allowed_order(order))) {
page = rmqueue_pcplist(preferred_zone, zone, order,
migratetype, alloc_flags);
@@ -4174,6 +4168,7 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
struct alloc_context *ac)
{
bool can_direct_reclaim = gfp_mask & __GFP_DIRECT_RECLAIM;
+ bool nofail = gfp_mask & __GFP_DIRECT_RECLAIM;
bool can_compact = gfp_compaction_allowed(gfp_mask);
const bool costly_order = order > PAGE_ALLOC_COSTLY_ORDER;
struct page *page = NULL;
@@ -4187,6 +4182,25 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
unsigned int zonelist_iter_cookie;
int reserve_flags;
+ if (nofail) {
+ /*
+ * We most definitely don't want callers attempting to
+ * allocate greater than order-1 page units with __GFP_NOFAIL.
+ */
+ WARN_ON_ONCE(order > 1);
+ /*
+ * Also we don't support __GFP_NOFAIL without __GFP_DIRECT_RECLAIM,
+ * otherwise, we may result in lockup.
+ */
+ WARN_ON_ONCE(!can_direct_reclaim);
+ /*
+ * PF_MEMALLOC request from this context is rather bizarre
+ * because we cannot reclaim anything and only can loop waiting
+ * for somebody to do a work for us.
+ */
+ WARN_ON_ONCE(current->flags & PF_MEMALLOC);
+ }
+
restart:
compaction_retries = 0;
no_progress_loops = 0;
@@ -4404,29 +4418,15 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
* Make sure that __GFP_NOFAIL request doesn't leak out and make sure
* we always retry
*/
- if (gfp_mask & __GFP_NOFAIL) {
+ if (nofail) {
/*
- * All existing users of the __GFP_NOFAIL are blockable, so warn
- * of any new users that actually require GFP_NOWAIT
+ * Lacking direct_reclaim we can't do anything to reclaim memory,
+ * we disregard these unreasonable nofail requests and still
+ * return NULL
*/
- if (WARN_ON_ONCE_GFP(!can_direct_reclaim, gfp_mask))
+ if (!can_direct_reclaim)
goto fail;
- /*
- * PF_MEMALLOC request from this context is rather bizarre
- * because we cannot reclaim anything and only can loop waiting
- * for somebody to do a work for us
- */
- WARN_ON_ONCE_GFP(current->flags & PF_MEMALLOC, gfp_mask);
-
- /*
- * non failing costly orders are a hard requirement which we
- * are not prepared for much so let's warn about these users
- * so that we can identify them and convert them to something
- * else.
- */
- WARN_ON_ONCE_GFP(costly_order, gfp_mask);
-
/*
* Help non-failing allocations by giving some access to memory
* reserves normally used for high priority non-blocking
> >
> > --
> > Michal Hocko
> > SUSE Labs
Thanks
Barry
