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

[Hao Ge]

On 2026/6/20 02:08, Suren Baghdasaryan wrote:
> On Fri, Jun 19, 2026 at 4:57 AM Brendan Jackman
> <brendan.jackman@xxxxxxxxx> 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@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.
> > > > 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