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

["Brendan Jackman" <brendan.jackman@linux.dev>]

On Mon Jun 22, 2026 at 1:58 AM UTC, Hao Ge wrote:
>
> On 2026/6/20 02:08, Suren Baghdasaryan wrote:
>> On Fri, Jun 19, 2026 at 4:57 AM Brendan Jackman
>> <brendan.jackman@linux.dev> wrote:
>>> On Thu Jun 18, 2026 at 2:22 AM UTC, Hao Ge wrote:
>>>> On 2026/6/18 01:14, Brendan Jackman wrote:
>>>>> On Wed Jun 17, 2026 at 4:49 PM UTC, Suren Baghdasaryan wrote:
>>>>>> On Wed, Jun 17, 2026 at 9:39 AM Vlastimil Babka (SUSE)
>>>>>> <vbabka@kernel.org> 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@gmail.com/
>>>>>>>
>>>>>>> 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.
>>>>> Ack. I'll aim to send that tomorrow once Sashiko has caught up.
>>>>>
>>>>>>>> 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
>>>>> Nice, this actually looks trivial? I can probably just tack it onto the
>>>>> v2 for this patch/series.
>>>>>
>>>>>> 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.
>>>>
>>>> Hi Brendan, Suren,
>>>>
>>>> Thanks for CC'ing me, Suren. This is indeed a viable approach
>>>>
>>>> and I believe it brings us one step closer to removing
>>>>
>>>> __GFP_NO_CODETAG entirely.
>>>>
>>>>
>>>> Brendan, I'd actually put together a rough local implementation
>>>>
>>>> earlier with mostly the same core idea as yours, and this change
>>>>
>>>> would indeed be minimal based on your patch.
>>>>
>>>> Thanks a lot for being interested in tacking this into your v2 patch series.
>>> Oh, I just took a look and it's a bit more fiddly than I thought because
>>> alloc_tag.c is actually in lib/ not mm/.
>
> Hi Suren and Bredan
>
>
>> One option is to move alloc_tag.c into mm/ (while keeping more generic
>> codetag.c in lib/). From a quick look, that seems doable and probably
>> the easiest approach.
>>
>>> How did you tackle that, can you share your implementation? It would be
>>> nice if we can avoid exposing alloc_flags in gfp.h.
>
> First, I introduced the ALLOC_NO_CODETAG flag as shown below:
>
> @@ -1478,6 +1480,7 @@ unsigned int reclaim_clean_pages_from_list(struct 
> zone *zone,
>   #define ALLOC_HIGHATOMIC       0x200 /* Allows access to 
> MIGRATE_HIGHATOMIC */
>   #define ALLOC_TRYLOCK          0x400 /* Only use spin_trylock in 
> allocation path */
>   #define ALLOC_KSWAPD           0x800 /* allow waking of kswapd, 
> __GFP_KSWAPD_RECLAIM set */
> +#define ALLOC_NO_CODETAG       0x1000 /* skip codetag tracking for this 
> allocation */
>
>
> Then, mirroring __alloc_pages_noprof, we wrapped a helper function named 
> alloc_pages_noprof_notag.
>
>
> @@ -5252,13 +5335,25 @@ 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;
>   }
>   EXPORT_SYMBOL(__alloc_pages_noprof);
>
> +struct page *alloc_pages_noprof_notag(gfp_t gfp, unsigned int order)
> +{
> +       struct page *page;
> +
> +       page = __alloc_frozen_pages_noprof(gfp, order, numa_node_id(), NULL,
> +                                          ALLOC_NO_CODETAG);
> +       if (page)
> +               set_page_refcounted(page);
> +       return page;
> +}
> +EXPORT_SYMBOL_GPL(alloc_pages_noprof_notag);
>
>
> Lastly, we exported this function in gfp.h as shown below:
>
>
> diff --git a/include/linux/gfp.h b/include/linux/gfp.h
> index 51ef13ed756e..ac6e837ac8c0 100644
> --- a/include/linux/gfp.h
> +++ b/include/linux/gfp.h
> @@ -234,6 +234,9 @@ struct folio *__folio_alloc_noprof(gfp_t gfp, 
> unsigned int order, int preferred_
>                  nodemask_t *nodemask);
>   #define __folio_alloc(...) alloc_hooks(__folio_alloc_noprof(__VA_ARGS__))
>
> +struct page *alloc_pages_noprof_notag(gfp_t gfp, unsigned int order);
> +#define alloc_pages_notag(...) 
> alloc_hooks(alloc_pages_noprof_notag(__VA_ARGS__))
>
>
> Hope this information helps you.

Cool, thanks! On Friday I also tried doing it by just moving the .c
file and that also seems to be pretty practical.