On Sat 31-08-24 08:28:23, Barry Song wrote:
> From: Barry Song <v-songbaohua@xxxxxxxx>
>
> 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 <vbabka@xxxxxxx>
> Signed-off-by: Barry Song <v-songbaohua@xxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
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.
> ---
> 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
