Re: [PATCH v2 13/13] mm: remove __GFP_NO_CODETAG

[Suren Baghdasaryan]

On Tue, Jun 23, 2026 at 12:57 AM Hao Ge <hao.ge@xxxxxxxxx> wrote:
>
> Hi Brendan
>
>
> On 2026/6/22 18:01, Brendan Jackman wrote:
> > Now that alloc_pages has an entrypoint that allows passing alloc_flags,
> > we can take advantage of this to start removing GFP flags that are only
> > used for mm-internal stuff.
> >
> > This requires also plumbing the alloc_flags into some more of the
> > allocator code, in particular __alloc_pages[_noprof]() gets an
> > alloc_flags arg to go along with its callees, and we now need to pass
> > those flags deeper into the allocator so they can reach the alloc_tag
> > code.
> >
> > To try and keep the new ALLOC_NO_CODETAG's scope nice and narrow, don't
> > define it in mm/internal.h, instead just define a "reserved bit" and
> > then use that in places that don't care about what it means.

I don't understand why you want to narrow down visibility of one of
the alloc_flag bits. We don't do that for any other flags, and this
seems like an unnecessary complexity.

> >
> > Signed-off-by: Brendan Jackman <jackmanb@xxxxxxxxxx>
>
>
> Nit: The title says "remove __GFP_NO_CODETAG" but the flag isn't really
> removed — it's migrated from gfp_t to alloc_flags as
>
> ALLOC_NO_CODETAG. Something like "mm: replace __GFP_NO_CODETAG with an
> alloc_flag" would be more accurate.
>
>
> Additionally, as Lorenzo pointed out in another thread, you will likely
> need to rebase this series later.
>
> I noticed Vlastimil has already landed the slab changes removing
> __GFP_NO_OBJ_EXT into mainline:
>
> https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=335c347686e76df9d2c7d7f61b5ea627a4c5cb4c
>
> For v3, it might make sense to fold in Vlastimil's patch so the full
> removal of __GFP_NO_OBJ_EXT can be completed end-to-end
>
> https://lore.kernel.org/all/20260609-slab_alloc_flags-v1-15-2bf4a4b9b526@xxxxxxxxxx/

I think Vlastimil's patch will be merged before this one, so this
patch could remove __GFP_NO_OBJ_EXT complely, saying that its last
user (__GFP_NO_CODETAG) is gone.

>
>
> > ---
> >   mm/alloc_tag.c       | 18 ++++++++++--------
> >   mm/compaction.c      |  4 ++--
> >   mm/internal.h        |  8 ++++++--
> >   mm/page_alloc.c      | 42 ++++++++++++++++++++++++------------------
> >   mm/page_frag_cache.c |  4 ++--
> >   5 files changed, 44 insertions(+), 32 deletions(-)
> >
> > diff --git a/mm/alloc_tag.c b/mm/alloc_tag.c
> > index d9be1cf5187d9..61a6cba32ff35 100644
> > --- a/mm/alloc_tag.c
> > +++ b/mm/alloc_tag.c
> > @@ -15,6 +15,8 @@
> >   #include <linux/vmalloc.h>
> >   #include <linux/kmemleak.h>
> >
> > +#include "internal.h"
> > +
> >   #define ALLOCINFO_FILE_NAME         "allocinfo"
> >   #define MODULE_ALLOC_TAG_VMAP_SIZE  (100000UL * sizeof(struct alloc_tag))
> >   #define SECTION_START(NAME)         (CODETAG_SECTION_START_PREFIX NAME)
> > @@ -785,16 +787,15 @@ struct pfn_pool {
> >                                        sizeof(unsigned long))
> >
> >   /*
> > - * Skip early PFN recording for a page allocation.  Reuses the
> > - * %__GFP_NO_OBJ_EXT bit.  Used by __alloc_tag_add_early_pfn() to avoid
> > - * recursion when allocating pages for the early PFN tracking list
> > - * itself.
> > + * Skip early PFN recording for a page allocation.  Used by
> > + * __alloc_tag_add_early_pfn() to avoid recursion when allocating pages for the
> > + * early PFN tracking list itself.
> >    *
> >    * Codetags of the pages allocated with __GFP_NO_CODETAG should be
> >    * cleared (via clear_page_tag_ref()) before freeing the pages to prevent
> >    * alloc_tag_sub_check() from triggering a warning.
> >    */
> > -#define __GFP_NO_CODETAG             __GFP_NO_OBJ_EXT
> > +#define ALLOC_NO_CODETAG             __ALLOC_ALLOC_TAG
> >
> >   static struct pfn_pool *current_pfn_pool __initdata;
> >
> > @@ -806,7 +807,8 @@ static void __init __alloc_tag_add_early_pfn(unsigned long pfn)
> >       do {
> >               pool = READ_ONCE(current_pfn_pool);
> >               if (!pool || atomic_read(&pool->count) >= PFN_POOL_SIZE) {
> > -                     struct page *new_page = alloc_page(__GFP_HIGH | __GFP_NO_CODETAG);
> > +                     struct page *new_page = __alloc_pages(__GFP_HIGH, 0, numa_mem_id(),
> > +                                                           NULL, ALLOC_NO_CODETAG);
> >                       struct pfn_pool *new;
> >
> >                       if (!new_page) {
> > @@ -837,7 +839,7 @@ typedef void alloc_tag_add_func(unsigned long pfn);
> >   static alloc_tag_add_func __rcu *alloc_tag_add_early_pfn_ptr __refdata =
> >       RCU_INITIALIZER(__alloc_tag_add_early_pfn);
> >
> > -void alloc_tag_add_early_pfn(unsigned long pfn, gfp_t gfp_flags)
> > +void alloc_tag_add_early_pfn(unsigned long pfn, unsigned int alloc_flags)
>
>
> alloc_tag_add_early_pfn is actually declared in include/linux/alloc_tag.h,
>
> so we need to update this header in sync as well.
>
> include/linux/alloc_tag.h:166:void alloc_tag_add_early_pfn(unsigned long
> pfn, gfp_t gfp_flags);
> include/linux/alloc_tag.h:170:static inline void
> alloc_tag_add_early_pfn(unsigned long pfn, gfp_t gfp_flags) {}
>
>
> >   {
> >       alloc_tag_add_func *alloc_tag_add;
> >
> > @@ -845,7 +847,7 @@ void alloc_tag_add_early_pfn(unsigned long pfn, gfp_t gfp_flags)
> >               return;
> >
> >       /* Skip allocations for the tracking list itself to avoid recursion. */
> > -     if (gfp_flags & __GFP_NO_CODETAG)
> > +     if (alloc_flags & ALLOC_NO_CODETAG)
> >               return;
> >
> >       rcu_read_lock();
> > diff --git a/mm/compaction.c b/mm/compaction.c
> > index b776f35ad0200..e90ebd2c54f48 100644
> > --- a/mm/compaction.c
> > +++ b/mm/compaction.c
> > @@ -82,7 +82,7 @@ static inline bool is_via_compact_memory(int order) { return false; }
> >
> >   static struct page *mark_allocated_noprof(struct page *page, unsigned int order, gfp_t gfp_flags)
> >   {
> > -     post_alloc_hook(page, order, __GFP_MOVABLE);
> > +     post_alloc_hook(page, order, __GFP_MOVABLE, ALLOC_DEFAULT);
> >       set_page_refcounted(page);
> >       return page;
> >   }
> > @@ -1850,7 +1850,7 @@ static struct folio *compaction_alloc_noprof(struct folio *src, unsigned long da
> >       }
> >       dst = (struct folio *)freepage;
> >
> > -     post_alloc_hook(&dst->page, order, __GFP_MOVABLE);
> > +     post_alloc_hook(&dst->page, order, __GFP_MOVABLE, ALLOC_DEFAULT);
> >       set_page_refcounted(&dst->page);
> >       if (order)
> >               prep_compound_page(&dst->page, order);
> > diff --git a/mm/internal.h b/mm/internal.h
> > index 0847b55bfc147..a45bedb9ada5f 100644
> > --- a/mm/internal.h
> > +++ b/mm/internal.h
> > @@ -684,6 +684,8 @@ struct alloc_context {
> >        */
> >       enum zone_type highest_zoneidx;
> >       bool spread_dirty_pages;
> > +     /* Only flags that are global to the whole allocation go here. */
> > +     unsigned int alloc_flags;
> >   };
> >
> >   /*
> > @@ -907,7 +909,8 @@ static inline void init_compound_tail(struct page *tail,
> >       prep_compound_tail(tail, head, order);
> >   }
> >
> > -void post_alloc_hook(struct page *page, unsigned int order, gfp_t gfp_flags);
> > +void post_alloc_hook(struct page *page, unsigned int order, gfp_t gfp_flags,
> > +                  unsigned int alloc_flags);
> >   extern bool free_pages_prepare(struct page *page, unsigned int order);
> >
> >   extern int user_min_free_kbytes;
> > @@ -1481,6 +1484,7 @@ unsigned int reclaim_clean_pages_from_list(struct zone *zone,
> >   #define ALLOC_HIGHATOMIC    0x200 /* Allows access to MIGRATE_HIGHATOMIC */
> >   #define ALLOC_NOLOCK                0x400 /* Only use spin_trylock in allocation path */
> >   #define ALLOC_KSWAPD                0x800 /* allow waking of kswapd, __GFP_KSWAPD_RECLAIM set */
> > +#define __ALLOC_ALLOC_TAG      0x1000 /* Reserved bit for use by alloc_tag code */
> >
> >   /* Flags that allow allocations below the min watermark. */
> >   #define ALLOC_RESERVES (ALLOC_NON_BLOCK|ALLOC_MIN_RESERVE|ALLOC_HIGHATOMIC|ALLOC_OOM)
> > @@ -1956,7 +1960,7 @@ bool may_expand_vm(struct mm_struct *mm, const vma_flags_t *vma_flags,
> >                  unsigned long npages);
> >
> >   struct page *__alloc_pages_noprof(gfp_t gfp, unsigned int order, int preferred_nid,
> > -             nodemask_t *nodemask);
> > +             nodemask_t *nodemask, unsigned int alloc_flags);
> >   #define __alloc_pages(...)                  alloc_hooks(__alloc_pages_noprof(__VA_ARGS__))
> >
> >   #endif      /* __MM_INTERNAL_H */
> > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > index d99e4ea8307ea..d50fd9c77a2e8 100644
> > --- a/mm/page_alloc.c
> > +++ b/mm/page_alloc.c
> > @@ -1246,7 +1246,7 @@ void __clear_page_tag_ref(struct page *page)
> >   /* Should be called only if mem_alloc_profiling_enabled() */
> >   static noinline
> >   void __pgalloc_tag_add(struct page *page, struct task_struct *task,
> > -                    unsigned int nr, gfp_t gfp_flags)
> > +                    unsigned int nr, unsigned int alloc_flags)
> >   {
> >       union pgtag_ref_handle handle;
> >       union codetag_ref ref;
> > @@ -1260,17 +1260,17 @@ void __pgalloc_tag_add(struct page *page, struct task_struct *task,
> >                * page_ext is not available yet, record the pfn so we can
> >                * clear the tag ref later when page_ext is initialized.
> >                */
> > -             alloc_tag_add_early_pfn(page_to_pfn(page), gfp_flags);
> > +             alloc_tag_add_early_pfn(page_to_pfn(page), alloc_flags);
> >               if (task->alloc_tag)
> >                       alloc_tag_set_inaccurate(task->alloc_tag);
> >       }
> >   }
> >
> >   static inline void pgalloc_tag_add(struct page *page, struct task_struct *task,
> > -                                unsigned int nr, gfp_t gfp_flags)
> > +                                unsigned int nr, unsigned int alloc_flags)
>
>
> The pgalloc_tag_add() stub in the non-CONFIG_MEM_ALLOC_PROFILING build
> could use the same parameter types for consistency

Umm, correction. It *should* use the same parameter type. It's
unfortunate that the compiler doesn't catch this...

>
>
> Thanks
>
> Best Regards
>
> Hao
>
>
> >   {
> >       if (mem_alloc_profiling_enabled())
> > -             __pgalloc_tag_add(page, task, nr, gfp_flags);
> > +             __pgalloc_tag_add(page, task, nr, alloc_flags);
> >   }
> >
> >   /* Should be called only if mem_alloc_profiling_enabled() */
> > @@ -1807,7 +1807,7 @@ static inline bool should_skip_init(gfp_t flags)
> >   }
> >
> >   inline void post_alloc_hook(struct page *page, unsigned int order,
> > -                             gfp_t gfp_flags)
> > +                             gfp_t gfp_flags, unsigned int alloc_flags)
> >   {
> >       const bool zero_tags = gfp_flags & __GFP_ZEROTAGS;
> >       bool init = !want_init_on_free() && want_init_on_alloc(gfp_flags) &&
> > @@ -1858,13 +1858,13 @@ inline void post_alloc_hook(struct page *page, unsigned int order,
> >
> >       set_page_owner(page, order, gfp_flags);
> >       page_table_check_alloc(page, order);
> > -     pgalloc_tag_add(page, current, 1 << order, gfp_flags);
> > +     pgalloc_tag_add(page, current, 1 << order, alloc_flags);
> >   }
> >
> >   static void prep_new_page(struct page *page, unsigned int order, gfp_t gfp_flags,
> >                                                       unsigned int alloc_flags)
> >   {
> > -     post_alloc_hook(page, order, gfp_flags);
> > +     post_alloc_hook(page, order, gfp_flags, alloc_flags);
> >
> >       if (order && (gfp_flags & __GFP_COMP))
> >               prep_compound_page(page, order);
> > @@ -4773,8 +4773,12 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
> >        * The fast path uses conservative alloc_flags to succeed only until
> >        * kswapd needs to be woken up, and to avoid the cost of setting up
> >        * alloc_flags precisely. So we do that now.
> > +      *
> > +      * Can't just or alloc_flags if it contains WMARK bits, but those flags
> > +      * shouldn't be set in ac->alloc_flags.
> >        */
> > -     alloc_flags = slowpath_alloc_flags(gfp_mask, order);
> > +     VM_WARN_ON(ac->alloc_flags & ALLOC_WMARK_MASK);
> > +     alloc_flags = ac->alloc_flags | slowpath_alloc_flags(gfp_mask, order);
> >
> >       /*
> >        * We need to recalculate the starting point for the zonelist iterator
> > @@ -4816,7 +4820,7 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
> >       reserve_flags = __gfp_pfmemalloc_flags(gfp_mask);
> >       if (reserve_flags)
> >               alloc_flags = cma_alloc_flags(gfp_mask, reserve_flags) |
> > -                                       (alloc_flags & ALLOC_KSWAPD);
> > +                             ac->alloc_flags | (alloc_flags & ALLOC_KSWAPD);
> >
> >       /*
> >        * Reset the nodemask and zonelist iterators if memory policies can be
> > @@ -5218,7 +5222,7 @@ unsigned long alloc_pages_bulk_noprof(gfp_t gfp, int preferred_nid,
> >       return nr_populated;
> >
> >   failed:
> > -     page = __alloc_pages_noprof(gfp, 0, preferred_nid, nodemask);
> > +     page = __alloc_pages_noprof(gfp, 0, preferred_nid, nodemask, ALLOC_DEFAULT);
> >       if (page)
> >               page_array[nr_populated++] = page;
> >       goto out;
> > @@ -5326,11 +5330,13 @@ struct page *__alloc_frozen_pages_noprof(gfp_t gfp, unsigned int order,
> >   {
> >       struct page *page;
> >       gfp_t alloc_gfp; /* The gfp_t that was actually used for allocation */
> > -     struct alloc_context ac = { };
> > +     struct alloc_context ac = {
> > +             .alloc_flags = alloc_flags,
> > +     };
> >       unsigned int fastpath_alloc_flags = alloc_flags;
> >
> >       /* Other flags could be supported later if needed. */
> > -     if (WARN_ON(alloc_flags & ~ALLOC_NOLOCK))
> > +     if (WARN_ON(alloc_flags & ~(ALLOC_NOLOCK | __ALLOC_ALLOC_TAG)))
> >               return NULL;
> >
> >       if (!alloc_order_allowed(gfp, order, alloc_flags))
> > @@ -5398,12 +5404,12 @@ struct page *__alloc_frozen_pages_noprof(gfp_t gfp, unsigned int order,
> >   EXPORT_SYMBOL(__alloc_frozen_pages_noprof);
> >
> >   struct page *__alloc_pages_noprof(gfp_t gfp, unsigned int order,
> > -             int preferred_nid, nodemask_t *nodemask)
> > +             int preferred_nid, nodemask_t *nodemask, unsigned int alloc_flags)
> >   {
> >       struct page *page;
> >
> >       page = __alloc_frozen_pages_noprof(gfp, order, preferred_nid, nodemask,
> > -                                        ALLOC_DEFAULT);
> > +                                        alloc_flags);
> >       if (page)
> >               set_page_refcounted(page);
> >       return page;
> > @@ -5418,14 +5424,14 @@ struct page *alloc_pages_node_noprof(int nid, gfp_t gfp_mask, unsigned int order
> >       VM_BUG_ON(nid < 0 || nid >= MAX_NUMNODES);
> >       warn_if_node_offline(nid, gfp_mask);
> >
> > -     return __alloc_pages_noprof(gfp_mask, order, nid, NULL);
> > +     return __alloc_pages_noprof(gfp_mask, order, nid, NULL, ALLOC_DEFAULT);
> >   }
> >
> >   struct folio *__folio_alloc_noprof(gfp_t gfp, unsigned int order, int preferred_nid,
> >               nodemask_t *nodemask)
> >   {
> >       struct page *page = __alloc_pages_noprof(gfp | __GFP_COMP, order,
> > -                                     preferred_nid, nodemask);
> > +                                     preferred_nid, nodemask, ALLOC_DEFAULT);
> >       return page_rmappable_folio(page);
> >   }
> >   EXPORT_SYMBOL(__folio_alloc_noprof);
> > @@ -7107,7 +7113,7 @@ static void split_free_frozen_pages(struct list_head *list, gfp_t gfp_mask)
> >               list_for_each_entry_safe(page, next, &list[order], lru) {
> >                       int i;
> >
> > -                     post_alloc_hook(page, order, gfp_mask);
> > +                     post_alloc_hook(page, order, gfp_mask, ALLOC_DEFAULT);
> >                       if (!order)
> >                               continue;
> >
> > @@ -7312,7 +7318,7 @@ int alloc_contig_frozen_range_noprof(unsigned long start, unsigned long end,
> >               struct page *head = pfn_to_page(start);
> >
> >               check_new_pages(head, order);
> > -             prep_new_page(head, order, gfp_mask, 0);
> > +             prep_new_page(head, order, gfp_mask, ALLOC_DEFAULT);
> >       } else {
> >               ret = -EINVAL;
> >               WARN(true, "PFN range: requested [%lu, %lu), allocated [%lu, %lu)\n",
> > diff --git a/mm/page_frag_cache.c b/mm/page_frag_cache.c
> > index d2423f30577e4..d9573170e0719 100644
> > --- a/mm/page_frag_cache.c
> > +++ b/mm/page_frag_cache.c
> > @@ -57,10 +57,10 @@ static struct page *__page_frag_cache_refill(struct page_frag_cache *nc,
> >       gfp_mask = (gfp_mask & ~__GFP_DIRECT_RECLAIM) |  __GFP_COMP |
> >                  __GFP_NOWARN | __GFP_NORETRY | __GFP_NOMEMALLOC;
> >       page = __alloc_pages(gfp_mask, PAGE_FRAG_CACHE_MAX_ORDER,
> > -                          numa_mem_id(), NULL);
> > +                          numa_mem_id(), NULL, ALLOC_DEFAULT);
> >   #endif
> >       if (unlikely(!page)) {
> > -             page = __alloc_pages(gfp, 0, numa_mem_id(), NULL);
> > +             page = __alloc_pages(gfp, 0, numa_mem_id(), NULL, ALLOC_DEFAULT);
> >               order = 0;
> >       }
> >
> >