Re: [RFC PATCH 00/16] Page Alloc Hogger
From: Lorenzo Stoakes (ARM)
Date: Fri Jul 31 2026 - 08:47:26 EST
On Tue, Jul 28, 2026 at 05:36:03PM -0700, Juan Yescas wrote:
> On Tue, Jul 28, 2026 at 12:29 PM David Hildenbrand (Arm)
> <david@xxxxxxxxxx> wrote:
> >
> > On 7/23/26 09:47, Juan Yescas wrote:
> > > This patch series introduces the Page Alloc Hogger. The Page Alloc Hogger
> > > allows you to allocate memory pages from specific nodes, zones, migration
> > > types, and orders directly via debugfs. This provides key benefits for
> > > testing and debugging:
> >
> > Would it be feasible to carry this as an OOT debugging module? Would a lot of
> > symbols be missing to achieve that?
> >
>
> Thanks David for the comment.
>
> The only symbol that would be needed to have this module as OOT is
> "migratetype_names".
Hmm I could have sworn I replied to this :)
Anyway, I don't think there's any need to export this. It's not like we're going
to radically rename them, and you'd probably have to update your module anyway
if we added a new migratetype.
So this being wholly contained in a module with no core changes seems the best
way?
Cheers, Lorenzo
>
> However, although this module was originally designed to debug CMA
> issues, it can be
> easily used to debug issues in kswapd, direct reclaims, OOM killer,
> etc. We could even
> use this module to add kunit test cases.
>
> Let's take for example this case. We want to allocate Unmovable memory and check
> that the allocation came from Movable, as per the buddy allocator
> fallback mechanism.
> How can we do that in user space?
>
> $ cat /proc/pagetypeinfo
> Page block order: 9
> Pages per block: 512
>
> Free pages count per migrate type at order 0 1 2 3 4 5 6 7 8 9 10
> Node 0, zone DMA, type Unmovable 0 0 0 0 0 0 0 0 0 0 0
> Node 0, zone DMA, type Movable 1 1 1 0 1 1 2 2 1 3 732
> Node 0, zone DMA, type Reclaimable 0 0 0 0 0 0 0 0 0 0 0
> Node 0, zone DMA, type HighAtomic 0 0 0 0 0 0 0 0 0 0 0
> Node 0, zone DMA, type CMA 0 0 0 0 0 0 0 0 0 1 7
> Node 0, zone DMA, type Isolate 0 0 0 0 0 0 0 0 0 0 0
> Node 0, zone Normal, type Unmovable 13 7 0 1 0 0 1 0 1 0 0
> Node 0, zone Normal, type Movable 1 1 1 1 1 1 1 0 1 1 1221
> Node 0, zone Normal, type Reclaimable 1 0 0 0 0 0 1 0 0 1 0
> Node 0, zone Normal, type HighAtomic 0 0 0 0 0 0 0 0 0 0 0
> Node 0, zone Normal, type CMA 0 0 0 0 0 0 0 0 0 1 7
> Node 0, zone Normal, type Isolate 0 0 0 0 0 0 0 0 0 0 0
>
> // Allocate Unmovable memory (note that there are NO Unmovable pages,
> so the allocation will fall back from Movable)
> $ echo 1221 > /sys/kernel/debug/mm/node-0/zone-Normal/order-10/migrate-Unmovable/nr_pages_allocs
>
> $ cat /proc/pagetypeinfo
> Page block order: 9
> Pages per block: 512
>
> Free pages count per migrate type at order 0 1 2
> 3 4 5 6 7 8 9 10
> Node 0, zone DMA, type Unmovable 0 0 0
> 0 0 0 0 0 0 0 0
> Node 0, zone DMA, type Movable 1 1 1
> 0 1 1 2 2 1 3 701
> Node 0, zone DMA, type Reclaimable 0 0 0
> 0 0 0 0 0 0 0 0
> Node 0, zone DMA, type HighAtomic 0 0 0
> 0 0 0 0 0 0 0 0
> Node 0, zone DMA, type CMA 0 0 0
> 0 0 0 0 0 0 1 31
> Node 0, zone DMA, type Isolate 0 0 0
> 0 0 0 0 0 0 0 0
> Node 0, zone Normal, type Unmovable 1 0 0
> 1 1 1 1 1 1 0 0
> Node 0, zone Normal, type Movable 1 0 1
> 1 1 1 1 1 1 1 7
> Node 0, zone Normal, type Reclaimable 0 1 0
> 0 1 0 0 0 1 0 0
> Node 0, zone Normal, type HighAtomic 0 0 0
> 0 0 0 0 0 0 0 0
> Node 0, zone Normal, type CMA 0 0 0
> 0 0 0 0 0 0 1 7
> Node 0, zone Normal, type Isolate 0 0 0
> 0 0 0 0 0 0 0 0
>
> Number of blocks type Unmovable Movable Reclaimable
> HighAtomic CMA Isolate
> Node 0, zone DMA 14 1458 0
> 0 64 0
> Node 0, zone Normal 2440 102 2
> 0 16 0
>
> // Now we want to test that Reclaimable memory allocations fall back
> from ZONE_DMA and Migrate Movable
>
> $ echo 600 > /sys/kernel/debug/mm/node-0/zone-Normal/order-10/migrate-Reclaimable/nr_pages_allocs
> # cat /proc/pagetypeinfo
> Page block order: 9
> Pages per block: 512
>
> Free pages count per migrate type at order 0 1 2
> 3 4 5 6 7 8 9 10
> Node 0, zone DMA, type Unmovable 0 0 0
> 0 0 1 1 0 0 1 0
> Node 0, zone DMA, type Movable 1 1 1
> 0 1 1 2 2 1 3 99
> Node 0, zone DMA, type Reclaimable 1 0 0
> 1 0 0 1 0 1 1 0
> Node 0, zone DMA, type HighAtomic 0 0 0
> 0 0 0 0 0 0 0 0
> Node 0, zone DMA, type CMA 0 0 0
> 0 0 0 0 0 0 1 31
> Node 0, zone DMA, type Isolate 0 0 0
> 0 0 0 0 0 0 0 0
> Node 0, zone Normal, type Unmovable 1 0 0
> 1 1 1 1 1 1 0 0
> Node 0, zone Normal, type Movable 0 0 0
> 1 0 0 1 0 1 0 7
> Node 0, zone Normal, type Reclaimable 0 1 0
> 0 1 0 0 0 1 0 0
> Node 0, zone Normal, type HighAtomic 0 0 0
> 0 0 0 0 0 0 0 0
> Node 0, zone Normal, type CMA 0 0 0
> 0 0 0 0 0 0 1 7
> Node 0, zone Normal, type Isolate 0 0 0
> 0 0 0 0 0 0 0 0
>
> Number of blocks type Unmovable Movable Reclaimable
> HighAtomic CMA Isolate
> Node 0, zone DMA 16 254 1202
> 0 64 0
> Node 0, zone Normal 2440 102 2
> 0 16 0
>
> // Now, we want to free all the MIGRATE_UNMOVABLE allocations and
> sleep 1 second for every
> // allocation and see how the pages return to the MIGRATE_UNMOVABLE bucket:
>
> for i in `seq 1 1221`; do echo $i > /sys/kernel/debug/mm/free; sleep 10; done
>
> // in another console
>
> watch cat /proc/pagetypeinfo
> 2026-07-29 00:28:49
>
> Page block order: 9
> Pages per block: 512
>
> Free pages count per migrate type at order 0 1 2
> 3 4 5 6 7 8 9 10
> Node 0, zone DMA, type Unmovable 0 0 0
> 0 0 1 1 0 0 1 0
> Node 0, zone DMA, type Movable 1 1 1
> 0 1 1 2 2 1 3 99
> Node 0, zone DMA, type Reclaimable 1 0 0
> 1 0 0 1 0 1 1 0
> Node 0, zone DMA, type HighAtomic 0 0 0
> 0 0 0 0 0 0 0 0
> Node 0, zone DMA, type CMA 0 0 0
> 0 0 0 0 0 0 1 31
> Node 0, zone DMA, type Isolate 0 0 0
> 0 0 0 0 0 0 0 0
> Node 0, zone Normal, type Unmovable 1 0 0
> 1 1 1 1 1 1 0 698
> Node 0, zone Normal, type Movable 1 0 0
> 1 0 0 0 0 1 0 7
> Node 0, zone Normal, type Reclaimable 0 1 0
> 0 1 0 0 0 1 0 0
> Node 0, zone Normal, type HighAtomic 0 0 0
> 0 0 0 0 0 0 0 0
> Node 0, zone Normal, type CMA 0 0 0
> 0 0 0 0 0 0 1 7
> Node 0, zone Normal, type Isolate 0 0 0
> 0 0 0 0 0 0 0 0
>
> Number of blocks type Unmovable Movable Reclaimable
> HighAtomic CMA Isolate
> Node 0, zone DMA 16 254 1202
> 0 64 0
> Node 0, zone Normal 2440 102 2
> 0 16 0
>
> Achieving the same result in a user program is not as straightforward.
>
> The Page Alloc Hogger gives us the flexibility to allocate from any
> valid memory we desire.
>
> As I mentioned before, it allows us to test/check/analyze/generate:
>
> - kwapd triggers
> - direct reclaims
> - OOM killer
> - generate page fragmentation using simple scripts instead of complex programs
>
> Greetigns
>
> Juan
>
>
> > --
> > Cheers,
> >
> > David
--
Cheers, Lorenzo