Re: [PATCH] mm/page_alloc: unify __alloc_frozen_pages[_nolock]_noprof()

[Suren Baghdasaryan]

On Wed, Jun 17, 2026 at 9:39 AM Vlastimil Babka (SUSE)
<vbabka@xxxxxxxxxx> wrote:
>
> +Cc Alexei
>
> On 6/17/26 17:29, Brendan Jackman wrote:
> > Currently the core allocator code is controlled by ALLOC_NOLOCK, but the
>
> It's not, it's ALLOC_TRYLOCK! Thanks for proving that we need to rename it
> to ALLOC_NOLOCK:
>
> https://lore.kernel.org/all/DJ9QPTO2WXNB.10E88ZHWRDHB0@xxxxxxxxx/
>
> So you just won the job to do the rename :) I think it should be done before
> this patch, so that the new usages and other _trylock names introduced here
> can be done as _nolock outright.
>
> > main entry point function is significantly different from the normal
> > __alloc_frozen_pages_nolock(), this is tiring when reading the code.
> >
> > Plumb the ALLOC_NOLOCK control one layer up in the call stack: create
> > an alloc_flags argument to __alloc_frozen_pages_nolock() (which is only
> > exposed to mm/) and then turn the nolock variant into a thin wrapper
> > that just sets that flag (as well as handling NUMA_NO_NODE, similar to
> > how some of the wrappers in gfp.h do).
> >
> > Rationale that this doesn't change anything:
> >
> > 1. Simple bits: A bunch of the nolock-specific handling is just moved to
> >    the new alloc_order_allowed(), alloc_trylock_allowed() and
> >    gfp_trylock.
> >
> > 2. __alloc_frozen_pages_noprof() has some extra logic that wasn't
> >    previously in the nolock variant:
> >
> >    a. Application of gfp_allowed_mask; this only affects early boot, and
> >       only flags that affect the slowpath get changed here.
> >
> >    b. Application of current_gfp_context() - also only affects the
> >       slowpath
> >
> > 3. The slowpath itself: this is now just explicitly skipped under
> >    !ALLOC_TRYLOCK.
>
> I'll have to ponder it more closely.
>
> > Ulterior motive: adding an alloc_flags arg to the allocator's
> > mm-internal entrypoint can later be used to do more allocation
> > customisation without needing to create new GFP flags.
>
> Ack.

I think this change might also help us in removing __GFP_NO_CODETAG
introduced in [1] and being the only user of __GFP_NO_OBJ_EXT once
Vlastimil's patchset removing other __GFP_NO_OBJ_EXT users lands.
CC'ing Hao as he is brainstorming ways to remove __GFP_NO_CODETAG, and
this might be the answer.

[1] https://lore.kernel.org/all/20260604024008.46592-1-hao.ge@xxxxxxxxx/

>
> > No functional change intended.
> >
> > Signed-off-by: Brendan Jackman <jackmanb@xxxxxxxxxx>
>
> Besides the need to ponder unintended effects, mostly LGTM. Just not a fan
> of the hardcoded '0' passed at various places. In the slab variant of this
> (the thread I've linked above) I went with SLAB_ALLOC_DEFAULT, so you can do
> e.g. ALLOC_DEFAULT here?
>
> > ---
> >  mm/hugetlb.c    |   2 +-
> >  mm/internal.h   |   4 +-
> >  mm/mempolicy.c  |   8 +--
> >  mm/page_alloc.c | 175 +++++++++++++++++++++++++++++---------------------------
> >  mm/slub.c       |   4 +-
> >  5 files changed, 99 insertions(+), 94 deletions(-)
> >
> > diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> > index 571212b80835e..619f6307dc98d 100644
> > --- a/mm/hugetlb.c
> > +++ b/mm/hugetlb.c
> > @@ -1806,7 +1806,7 @@ static struct folio *alloc_buddy_frozen_folio(int order, gfp_t gfp_mask,
> >       if (alloc_try_hard)
> >               gfp_mask |= __GFP_RETRY_MAYFAIL;
> >
> > -     folio = (struct folio *)__alloc_frozen_pages(gfp_mask, order, nid, nmask);
> > +     folio = (struct folio *)__alloc_frozen_pages(gfp_mask, order, nid, nmask, 0);
> >
> >       /*
> >        * If we did not specify __GFP_RETRY_MAYFAIL, but still got a
> > diff --git a/mm/internal.h b/mm/internal.h
> > index 181e79f1d6a20..1043eb833836c 100644
> > --- a/mm/internal.h
> > +++ b/mm/internal.h
> > @@ -913,7 +913,7 @@ extern bool free_pages_prepare(struct page *page, unsigned int order);
> >  extern int user_min_free_kbytes;
> >
> >  struct page *__alloc_frozen_pages_noprof(gfp_t, unsigned int order, int nid,
> > -             nodemask_t *);
> > +             nodemask_t *, unsigned int alloc_flags);
> >  #define __alloc_frozen_pages(...) \
> >       alloc_hooks(__alloc_frozen_pages_noprof(__VA_ARGS__))
> >  void free_frozen_pages(struct page *page, unsigned int order);
> > @@ -924,7 +924,7 @@ struct page *alloc_frozen_pages_noprof(gfp_t, unsigned int order);
> >  #else
> >  static inline struct page *alloc_frozen_pages_noprof(gfp_t gfp, unsigned int order)
> >  {
> > -     return __alloc_frozen_pages_noprof(gfp, order, numa_node_id(), NULL);
> > +     return __alloc_frozen_pages_noprof(gfp, order, numa_node_id(), NULL, 0);
> >  }
> >  #endif
> >
> > diff --git a/mm/mempolicy.c b/mm/mempolicy.c
> > index 36699fabd3c22..dccff90682035 100644
> > --- a/mm/mempolicy.c
> > +++ b/mm/mempolicy.c
> > @@ -2425,9 +2425,9 @@ static struct page *alloc_pages_preferred_many(gfp_t gfp, unsigned int order,
> >        */
> >       preferred_gfp = gfp | __GFP_NOWARN;
> >       preferred_gfp &= ~(__GFP_DIRECT_RECLAIM | __GFP_NOFAIL);
> > -     page = __alloc_frozen_pages_noprof(preferred_gfp, order, nid, nodemask);
> > +     page = __alloc_frozen_pages_noprof(preferred_gfp, order, nid, nodemask, 0);
> >       if (!page)
> > -             page = __alloc_frozen_pages_noprof(gfp, order, nid, NULL);
> > +             page = __alloc_frozen_pages_noprof(gfp, order, nid, NULL, 0);
> >
> >       return page;
> >  }
> > @@ -2475,7 +2475,7 @@ static struct page *alloc_pages_mpol(gfp_t gfp, unsigned int order,
> >                        */
> >                       page = __alloc_frozen_pages_noprof(
> >                               gfp | __GFP_THISNODE | __GFP_NORETRY, order,
> > -                             nid, NULL);
> > +                             nid, NULL, 0);
> >                       if (page || !(gfp & __GFP_DIRECT_RECLAIM))
> >                               return page;
> >                       /*
> > @@ -2487,7 +2487,7 @@ static struct page *alloc_pages_mpol(gfp_t gfp, unsigned int order,
> >               }
> >       }
> >
> > -     page = __alloc_frozen_pages_noprof(gfp, order, nid, nodemask);
> > +     page = __alloc_frozen_pages_noprof(gfp, order, nid, nodemask, 0);
> >
> >       if (unlikely(pol->mode == MPOL_INTERLEAVE ||
> >                    pol->mode == MPOL_WEIGHTED_INTERLEAVE) && page) {
> > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > index 0111cdbdb5321..fc4d07bbf44b5 100644
> > --- a/mm/page_alloc.c
> > +++ b/mm/page_alloc.c
> > @@ -5253,24 +5253,98 @@ void free_pages_bulk(struct page **page_array, unsigned long nr_pages)
> >       }
> >  }
> >
> > -/*
> > - * This is the 'heart' of the zoned buddy allocator.
> > - */
> > -struct page *__alloc_frozen_pages_noprof(gfp_t gfp, unsigned int order,
> > -             int preferred_nid, nodemask_t *nodemask)
> > +static inline bool alloc_order_allowed(gfp_t gfp, unsigned int order,
> > +                                    unsigned int alloc_flags)
> >  {
> > -     struct page *page;
> > -     unsigned int alloc_flags = ALLOC_WMARK_LOW;
> > -     gfp_t alloc_gfp; /* The gfp_t that was actually used for allocation */
> > -     struct alloc_context ac = { };
> > +
> > +     if (alloc_flags & ALLOC_TRYLOCK)
> > +             return pcp_allowed_order(order);
> >
> >       /*
> >        * There are several places where we assume that the order value is sane
> >        * so bail out early if the request is out of bound.
> >        */
> > -     if (WARN_ON_ONCE_GFP(order > MAX_PAGE_ORDER, gfp))
> > +     return !(WARN_ON_ONCE_GFP(order > MAX_PAGE_ORDER, gfp));
> > +}
> > +
> > +static inline bool alloc_trylock_allowed(void)
> > +{
> > +     /*
> > +      * In PREEMPT_RT spin_trylock() will call raw_spin_lock() which is
> > +      * unsafe in NMI. If spin_trylock() is called from hard IRQ the current
> > +      * task may be waiting for one rt_spin_lock, but rt_spin_trylock() will
> > +      * mark the task as the owner of another rt_spin_lock which will
> > +      * confuse PI logic, so return immediately if called from hard IRQ or
> > +      * NMI.
> > +      *
> > +      * Note, irqs_disabled() case is ok. This function can be called
> > +      * from raw_spin_lock_irqsave region.
> > +      */
> > +     if (IS_ENABLED(CONFIG_PREEMPT_RT) && (in_nmi() || in_hardirq()))
> > +             return false;
> > +
> > +     /* On UP, spin_trylock() always succeeds even when it is locked */
> > +     if (!IS_ENABLED(CONFIG_SMP) && in_nmi())
> > +             return false;
> > +
> > +     /* Bailout, since _deferred_grow_zone() needs to take a lock */
> > +     if (deferred_pages_enabled())
> > +             return false;
> > +
> > +     return true;
> > +}
> > +
> > +/*
> > + * GFP flags to set for ALLOC_TRYLOCK i.e. alloc_pages_nolock().
> > + *
> > + * Do not specify __GFP_DIRECT_RECLAIM, since direct claim is not allowed.
> > + * Do not specify __GFP_KSWAPD_RECLAIM either, since wake up of kswapd
> > + * is not safe in arbitrary context.
> > + *
> > + * These two are the conditions for gfpflags_allow_spinning() being true.
> > + *
> > + * Specify __GFP_NOWARN since failing alloc_pages_nolock() is not a reason
> > + * to warn. Also warn would trigger printk() which is unsafe from
> > + * various contexts. We cannot use printk_deferred_enter() to mitigate,
> > + * since the running context is unknown.
> > + *
> > + * Specify __GFP_ZERO to make sure that call to kmsan_alloc_page() below
> > + * is safe in any context. Also zeroing the page is mandatory for
> > + * BPF use cases.
> > + *
> > + * Though __GFP_NOMEMALLOC is not checked in the code path below,
> > + * specify it here to highlight that alloc_pages_nolock()
> > + * doesn't want to deplete reserves.
> > + */
> > +static const gfp_t gfp_trylock = __GFP_NOWARN | __GFP_ZERO | __GFP_NOMEMALLOC |
> > +                             __GFP_COMP;
> > +
> > +/*
> > + * This is the 'heart' of the zoned buddy allocator.
> > + */
> > +struct page *__alloc_frozen_pages_noprof(gfp_t gfp, unsigned int order,
> > +             int preferred_nid, nodemask_t *nodemask, unsigned int alloc_flags)
> > +{
> > +     struct page *page;
> > +     gfp_t alloc_gfp; /* The gfp_t that was actually used for allocation */
> > +     struct alloc_context ac = { };
> > +
> > +     /* Other flags could be supported later if needed. */
> > +     if (WARN_ON(alloc_flags & ~ALLOC_TRYLOCK))
> >               return NULL;
> >
> > +     if (!alloc_order_allowed(gfp, order, alloc_flags))
> > +             return NULL;
> > +
> > +     if (alloc_flags & ALLOC_TRYLOCK) {
> > +             VM_WARN_ON_ONCE(gfp & ~__GFP_ACCOUNT);
> > +             if (!alloc_trylock_allowed())
> > +                     return NULL;
> > +             gfp |= gfp_trylock;
> > +     } else {
> > +             alloc_flags |= ALLOC_WMARK_LOW;
> > +     }
> > +
> >       gfp &= gfp_allowed_mask;
> >       /*
> >        * Apply scoped allocation constraints. This is mainly about GFP_NOFS
> > @@ -5291,9 +5365,9 @@ struct page *__alloc_frozen_pages_noprof(gfp_t gfp, unsigned int order,
> >        */
> >       alloc_flags |= alloc_flags_nofragment(zonelist_zone(ac.preferred_zoneref), gfp);
> >
> > -     /* First allocation attempt */
> > +     /* First allocation attempt (or, for trylock, only attempt) */
> >       page = get_page_from_freelist(alloc_gfp, order, alloc_flags, &ac);
> > -     if (likely(page))
> > +     if (likely(page) || (alloc_flags & ALLOC_TRYLOCK))
> >               goto out;
> >
> >       alloc_gfp = gfp;
> > @@ -5310,7 +5384,8 @@ struct page *__alloc_frozen_pages_noprof(gfp_t gfp, unsigned int order,
> >  out:
> >       if (memcg_kmem_online() && (gfp & __GFP_ACCOUNT) && page &&
> >           unlikely(__memcg_kmem_charge_page(page, gfp, order) != 0)) {
> > -             free_frozen_pages(page, order);
> > +             __free_frozen_pages(page, order,
> > +                                 alloc_flags & ALLOC_TRYLOCK ? FPI_TRYLOCK : 0);
> >               page = NULL;
> >       }
> >
> > @@ -5326,7 +5401,7 @@ struct page *__alloc_pages_noprof(gfp_t gfp, unsigned int order,
> >  {
> >       struct page *page;
> >
> > -     page = __alloc_frozen_pages_noprof(gfp, order, preferred_nid, nodemask);
> > +     page = __alloc_frozen_pages_noprof(gfp, order, preferred_nid, nodemask, 0);
> >       if (page)
> >               set_page_refcounted(page);
> >       return page;
> > @@ -7856,80 +7931,10 @@ static bool __free_unaccepted(struct page *page)
> >
> >  struct page *alloc_frozen_pages_nolock_noprof(gfp_t gfp_flags, int nid, unsigned int order)
> >  {
> > -     /*
> > -      * Do not specify __GFP_DIRECT_RECLAIM, since direct claim is not allowed.
> > -      * Do not specify __GFP_KSWAPD_RECLAIM either, since wake up of kswapd
> > -      * is not safe in arbitrary context.
> > -      *
> > -      * These two are the conditions for gfpflags_allow_spinning() being true.
> > -      *
> > -      * Specify __GFP_NOWARN since failing alloc_pages_nolock() is not a reason
> > -      * to warn. Also warn would trigger printk() which is unsafe from
> > -      * various contexts. We cannot use printk_deferred_enter() to mitigate,
> > -      * since the running context is unknown.
> > -      *
> > -      * Specify __GFP_ZERO to make sure that call to kmsan_alloc_page() below
> > -      * is safe in any context. Also zeroing the page is mandatory for
> > -      * BPF use cases.
> > -      *
> > -      * Though __GFP_NOMEMALLOC is not checked in the code path below,
> > -      * specify it here to highlight that alloc_pages_nolock()
> > -      * doesn't want to deplete reserves.
> > -      */
> > -     gfp_t alloc_gfp = __GFP_NOWARN | __GFP_ZERO | __GFP_NOMEMALLOC | __GFP_COMP
> > -                     | gfp_flags;
> > -     unsigned int alloc_flags = ALLOC_TRYLOCK;
> > -     struct alloc_context ac = { };
> > -     struct page *page;
> > -
> > -     VM_WARN_ON_ONCE(gfp_flags & ~__GFP_ACCOUNT);
> > -     /*
> > -      * In PREEMPT_RT spin_trylock() will call raw_spin_lock() which is
> > -      * unsafe in NMI. If spin_trylock() is called from hard IRQ the current
> > -      * task may be waiting for one rt_spin_lock, but rt_spin_trylock() will
> > -      * mark the task as the owner of another rt_spin_lock which will
> > -      * confuse PI logic, so return immediately if called from hard IRQ or
> > -      * NMI.
> > -      *
> > -      * Note, irqs_disabled() case is ok. This function can be called
> > -      * from raw_spin_lock_irqsave region.
> > -      */
> > -     if (IS_ENABLED(CONFIG_PREEMPT_RT) && (in_nmi() || in_hardirq()))
> > -             return NULL;
> > -
> > -     /* On UP, spin_trylock() always succeeds even when it is locked */
> > -     if (!IS_ENABLED(CONFIG_SMP) && in_nmi())
> > -             return NULL;
> > -
> > -     if (!pcp_allowed_order(order))
> > -             return NULL;
> > -
> > -     /* Bailout, since _deferred_grow_zone() needs to take a lock */
> > -     if (deferred_pages_enabled())
> > -             return NULL;
> > -
> >       if (nid == NUMA_NO_NODE)
> >               nid = numa_node_id();
> >
> > -     prepare_alloc_pages(alloc_gfp, order, nid, NULL, &ac,
> > -                         &alloc_gfp, &alloc_flags);
> > -
> > -     /*
> > -      * Best effort allocation from percpu free list.
> > -      * If it's empty attempt to spin_trylock zone->lock.
> > -      */
> > -     page = get_page_from_freelist(alloc_gfp, order, alloc_flags, &ac);
> > -
> > -     /* Unlike regular alloc_pages() there is no __alloc_pages_slowpath(). */
> > -
> > -     if (memcg_kmem_online() && page && (gfp_flags & __GFP_ACCOUNT) &&
> > -         unlikely(__memcg_kmem_charge_page(page, alloc_gfp, order) != 0)) {
> > -             __free_frozen_pages(page, order, FPI_TRYLOCK);
> > -             page = NULL;
> > -     }
> > -     trace_mm_page_alloc(page, order, alloc_gfp, ac.migratetype);
> > -     kmsan_alloc_page(page, order, alloc_gfp);
> > -     return page;
> > +     return __alloc_frozen_pages_noprof(gfp_flags, order, nid, NULL, ALLOC_TRYLOCK);
> >  }
> >  /**
> >   * alloc_pages_nolock - opportunistic reentrant allocation from any context
> > diff --git a/mm/slub.c b/mm/slub.c
> > index a2bf3756ca7d0..b9fb66071bd07 100644
> > --- a/mm/slub.c
> > +++ b/mm/slub.c
> > @@ -3275,7 +3275,7 @@ static inline struct slab *alloc_slab_page(gfp_t flags, int node,
> >       else if (node == NUMA_NO_NODE)
> >               page = alloc_frozen_pages(flags, order);
> >       else
> > -             page = __alloc_frozen_pages(flags, order, node, NULL);
> > +             page = __alloc_frozen_pages(flags, order, node, NULL, 0);
> >
> >       if (!page)
> >               return NULL;
> > @@ -5236,7 +5236,7 @@ static void *___kmalloc_large_node(size_t size, gfp_t flags, int node)
> >       if (node == NUMA_NO_NODE)
> >               page = alloc_frozen_pages_noprof(flags, order);
> >       else
> > -             page = __alloc_frozen_pages_noprof(flags, order, node, NULL);
> > +             page = __alloc_frozen_pages_noprof(flags, order, node, NULL, 0);
> >
> >       if (page) {
> >               ptr = page_address(page);
> >
> > ---
> > base-commit: 1111012ec6508a38a39f8d20c213c8c9cf3c96c0
> > change-id: 20260617-alloc-trylock-14ad37dab337
> >
> > Best regards,
> > --
> > Brendan Jackman <jackmanb@xxxxxxxxxx>
> >
>