On Mon, Sep 2, 2024 at 7:58 PM Michal Hocko <mho...@suse.com> wrote:
>
> On Sat 31-08-24 08:28:23, Barry Song wrote:
> > From: Barry Song <v-songbao...@oppo.com>
> >
> > Three points for this change:
> >
> > 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. We don't 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 replace
> > WARN_ON_ONCE_GFP by WARN_ON_ONCE.
> >
> > Suggested-by: Vlastimil Babka <vba...@suse.cz>
> > Signed-off-by: Barry Song <v-songbao...@oppo.com>
>
> Acked-by: Michal Hocko <mho...@suse.com>
>
> Updating the doc about order > 1 sounds like it would still fall into
> the scope of this patch. I don not think we absolutely have to document
> each unsupported gfp flags combination for GFP_NOFAIL but the order is a
> good addition with a note that kvmalloc should be used instead in such a
> case.
Hi Andrew,
If there are no objections from Michal and David, could you please
squash the following:
>From fc7a2a49e8d0811d706d13d2080393274f316806 Mon Sep 17 00:00:00 2001
From: Barry Song <v-songbao...@oppo.com>
Date: Wed, 4 Sep 2024 10:26:19 +1200
Subject: [PATCH] mm: also update the doc for __GFP_NOFAIL with order > 1
Obviously we only support order <= 1 __GFP_NOFAIL allocation and if
someone wants larger memory, they should consider using kvmalloc()
instead.
Suggested-by: David Hildenbrand <da...@redhat.com>
Suggested-by: Michal Hocko <mho...@suse.com>
Signed-off-by: Barry Song <v-songbao...@oppo.com>
---
include/linux/gfp_types.h | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/include/linux/gfp_types.h b/include/linux/gfp_types.h
index 4a1fa7706b0c..65db9349f905 100644
--- a/include/linux/gfp_types.h
+++ b/include/linux/gfp_types.h
@@ -253,7 +253,8 @@ enum {
* used only when there is no reasonable failure policy) but it is
* definitely preferable to use the flag rather than opencode endless
* loop around allocator.
- * Using this flag for costly allocations is _highly_ discouraged.
+ * Allocating pages from the buddy with __GFP_NOFAIL and order > 1 is
+ * not supported. Please consider using kvmalloc() instead.
*/
#define __GFP_IO ((__force gfp_t)___GFP_IO)
#define __GFP_FS ((__force gfp_t)___GFP_FS)
--
2.34.1
>
> > ---
> > mm/page_alloc.c | 50 ++++++++++++++++++++++++-------------------------
> > 1 file changed, 25 insertions(+), 25 deletions(-)
> >
> > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > index c81ee5662cc7..e790b4227322 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);
> > @@ -4175,6 +4169,7 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int
> > order,
> > {
> > bool can_direct_reclaim = gfp_mask & __GFP_DIRECT_RECLAIM;
> > bool can_compact = gfp_compaction_allowed(gfp_mask);
> > + bool nofail = gfp_mask & __GFP_NOFAIL;
> > const bool costly_order = order > PAGE_ALLOC_COSTLY_ORDER;
> > struct page *page = NULL;
> > unsigned int alloc_flags;
> > @@ -4187,6 +4182,25 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int
> > order,
> > unsigned int zonelist_iter_cookie;
> > int reserve_flags;
> >
> > + if (unlikely(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 (unlikely(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
> > --
> > 2.34.1
>
> --
> Michal Hocko
> SUSE Labs
Thanks
Barry
