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

[Hao Ge <hao.ge@linux.dev>]

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.


Thanks

Best Regards

Hao