Re: [PATCH] mm/alloc_tag: clear codetag for pages allocated before page_ext initialization

Suren Baghdasaryan
2026-03-25T00:21:49Z

On Tue, Mar 24, 2026 at 2:43 AM Hao Ge <hao.ge@linux.dev> wrote:
>
>
> On 2026/3/24 06:47, Suren Baghdasaryan wrote:
> > On Mon, Mar 23, 2026 at 2:16 AM Hao Ge <hao.ge@linux.dev> wrote:
> >>
> >> On 2026/3/20 10:14, Suren Baghdasaryan wrote:
> >>> On Thu, Mar 19, 2026 at 6:58 PM Hao Ge <hao.ge@linux.dev> wrote:
> >>>> On 2026/3/20 07:48, Suren Baghdasaryan wrote:
> >>>>> On Thu, Mar 19, 2026 at 4:44 PM Suren Baghdasaryan <surenb@google.com> wrote:
> >>>>>> On Thu, Mar 19, 2026 at 3:28 PM Andrew Morton <akpm@linux-foundation.org> wrote:
> >>>>>>> On Thu, 19 Mar 2026 16:31:53 +0800 Hao Ge <hao.ge@linux.dev> wrote:
> >>>>>>>
> >>>>>>>> Due to initialization ordering, page_ext is allocated and initialized
> >>>>>>>> relatively late during boot. Some pages have already been allocated
> >>>>>>>> and freed before page_ext becomes available, leaving their codetag
> >>>>>>>> uninitialized.
> >>>>>> Hi Hao,
> >>>>>> Thanks for the report.
> >>>>>> Hmm. So, we are allocating pages before page_ext is initialized...
> >>>>>>
> >>>>>>>> A clear example is in init_section_page_ext(): alloc_page_ext() calls
> >>>>>>>> kmemleak_alloc().
> >>>>> Forgot to ask. The example you are using here is for page_ext
> >>>>> allocation itself. Do you have any other examples where page
> >>>>> allocation happens before page_ext initialization? If that's the only
> >>>>> place, then we might be able to fix this in a simpler way by doing
> >>>>> something special for alloc_page_ext().
> >>>> Hi Suren
> >>>>
> >>>> To help illustrate the point, here's the debug log I added:
> >>>>
> >>>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> >>>> index 2d4b6f1a554e..ebfe636f5b07 100644
> >>>> --- a/mm/page_alloc.c
> >>>> +++ b/mm/page_alloc.c
> >>>> @@ -1293,6 +1293,9 @@ void __pgalloc_tag_add(struct page *page, struct
> >>>> task_struct *task,
> >>>> alloc_tag_add(&ref, task->alloc_tag, PAGE_SIZE * nr);
> >>>> update_page_tag_ref(handle, &ref);
> >>>> put_page_tag_ref(handle);
> >>>> + } else {
> >>>> + pr_warn("__pgalloc_tag_add: get_page_tag_ref failed!
> >>>> page=%p pfn=%lu nr=%u\n", page, page_to_pfn(page), nr);
> >>>> + dump_stack();
> >>>> }
> >>>> }
> >>>>
> >>>>
> >>>> And I caught the following logs:
> >>>>
> >>>> [ 0.296399] __pgalloc_tag_add: get_page_tag_ref failed!
> >>>> page=ffffea000400c700 pfn=1049372 nr=1
> >>>> [ 0.296400] CPU: 0 UID: 0 PID: 0 Comm: swapper/0 Not tainted
> >>>> 7.0.0-rc4-dirty #12 PREEMPT(lazy)
> >>>> [ 0.296402] Hardware name: Red Hat KVM, BIOS
> >>>> rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
> >>>> [ 0.296402] Call Trace:
> >>>> [ 0.296403] <TASK>
> >>>> [ 0.296403] dump_stack_lvl+0x53/0x70
> >>>> [ 0.296405] __pgalloc_tag_add+0x3a3/0x6e0
> >>>> [ 0.296406] ? __pfx___pgalloc_tag_add+0x10/0x10
> >>>> [ 0.296407] ? kasan_unpoison+0x27/0x60
> >>>> [ 0.296409] ? __kasan_unpoison_pages+0x2c/0x40
> >>>> [ 0.296411] get_page_from_freelist+0xa54/0x1310
> >>>> [ 0.296413] __alloc_frozen_pages_noprof+0x206/0x4c0
> >>>> [ 0.296415] ? __pfx___alloc_frozen_pages_noprof+0x10/0x10
> >>>> [ 0.296417] ? stack_depot_save_flags+0x3f/0x680
> >>>> [ 0.296418] ? ___slab_alloc+0x518/0x530
> >>>> [ 0.296420] alloc_pages_mpol+0x13a/0x3f0
> >>>> [ 0.296421] ? __pfx_alloc_pages_mpol+0x10/0x10
> >>>> [ 0.296423] ? _raw_spin_lock_irqsave+0x8a/0xf0
> >>>> [ 0.296424] ? __pfx__raw_spin_lock_irqsave+0x10/0x10
> >>>> [ 0.296426] alloc_slab_page+0xc2/0x130
> >>>> [ 0.296427] allocate_slab+0x77/0x2c0
> >>>> [ 0.296429] ? syscall_enter_define_fields+0x3bb/0x5f0
> >>>> [ 0.296430] ___slab_alloc+0x125/0x530
> >>>> [ 0.296432] ? __trace_define_field+0x252/0x3d0
> >>>> [ 0.296433] __kmalloc_noprof+0x329/0x630
> >>>> [ 0.296435] ? syscall_enter_define_fields+0x3bb/0x5f0
> >>>> [ 0.296436] syscall_enter_define_fields+0x3bb/0x5f0
> >>>> [ 0.296438] ? __pfx_syscall_enter_define_fields+0x10/0x10
> >>>> [ 0.296440] event_define_fields+0x326/0x540
> >>>> [ 0.296441] __trace_early_add_events+0xac/0x3c0
> >>>> [ 0.296443] trace_event_init+0x24c/0x460
> >>>> [ 0.296445] trace_init+0x9/0x20
> >>>> [ 0.296446] start_kernel+0x199/0x3c0
> >>>> [ 0.296448] x86_64_start_reservations+0x18/0x30
> >>>> [ 0.296449] x86_64_start_kernel+0xe2/0xf0
> >>>> [ 0.296451] common_startup_64+0x13e/0x141
> >>>> [ 0.296453] </TASK>
> >>>>
> >>>>
> >>>> [ 0.312234] __pgalloc_tag_add: get_page_tag_ref failed!
> >>>> page=ffffea000400f900 pfn=1049572 nr=1
> >>>> [ 0.312234] CPU: 0 UID: 0 PID: 0 Comm: swapper/0 Not tainted
> >>>> 7.0.0-rc4-dirty #12 PREEMPT(lazy)
> >>>> [ 0.312236] Hardware name: Red Hat KVM, BIOS
> >>>> rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
> >>>> [ 0.312236] Call Trace:
> >>>> [ 0.312237] <TASK>
> >>>> [ 0.312237] dump_stack_lvl+0x53/0x70
> >>>> [ 0.312239] __pgalloc_tag_add+0x3a3/0x6e0
> >>>> [ 0.312240] ? __pfx___pgalloc_tag_add+0x10/0x10
> >>>> [ 0.312241] ? rmqueue.constprop.0+0x4fc/0x1ce0
> >>>> [ 0.312243] ? kasan_unpoison+0x27/0x60
> >>>> [ 0.312244] ? __kasan_unpoison_pages+0x2c/0x40
> >>>> [ 0.312246] get_page_from_freelist+0xa54/0x1310
> >>>> [ 0.312248] __alloc_frozen_pages_noprof+0x206/0x4c0
> >>>> [ 0.312250] ? __pfx___alloc_frozen_pages_noprof+0x10/0x10
> >>>> [ 0.312253] alloc_slab_page+0x39/0x130
> >>>> [ 0.312254] allocate_slab+0x77/0x2c0
> >>>> [ 0.312255] ? alloc_cpumask_var_node+0xc7/0x230
> >>>> [ 0.312257] ___slab_alloc+0x46d/0x530
> >>>> [ 0.312259] __kmalloc_node_noprof+0x2fa/0x680
> >>>> [ 0.312261] ? alloc_cpumask_var_node+0xc7/0x230
> >>>> [ 0.312263] alloc_cpumask_var_node+0xc7/0x230
> >>>> [ 0.312264] init_desc+0x141/0x6b0
> >>>> [ 0.312266] alloc_desc+0x108/0x1b0
> >>>> [ 0.312267] early_irq_init+0xee/0x1c0
> >>>> [ 0.312268] ? __pfx_early_irq_init+0x10/0x10
> >>>> [ 0.312271] start_kernel+0x1ab/0x3c0
> >>>> [ 0.312272] x86_64_start_reservations+0x18/0x30
> >>>> [ 0.312274] x86_64_start_kernel+0xe2/0xf0
> >>>> [ 0.312275] common_startup_64+0x13e/0x141
> >>>> [ 0.312277] </TASK>
> >>>>
> >>>> [ 0.312834] __pgalloc_tag_add: get_page_tag_ref failed!
> >>>> page=ffffea000400fc00 pfn=1049584 nr=1
> >>>> [ 0.312835] CPU: 0 UID: 0 PID: 0 Comm: swapper/0 Not tainted
> >>>> 7.0.0-rc4-dirty #12 PREEMPT(lazy)
> >>>> [ 0.312836] Hardware name: Red Hat KVM, BIOS
> >>>> rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
> >>>> [ 0.312837] Call Trace:
> >>>> [ 0.312837] <TASK>
> >>>> [ 0.312838] dump_stack_lvl+0x53/0x70
> >>>> [ 0.312840] __pgalloc_tag_add+0x3a3/0x6e0
> >>>> [ 0.312841] ? __pfx___pgalloc_tag_add+0x10/0x10
> >>>> [ 0.312842] ? rmqueue.constprop.0+0x4fc/0x1ce0
> >>>> [ 0.312844] ? kasan_unpoison+0x27/0x60
> >>>> [ 0.312845] ? __kasan_unpoison_pages+0x2c/0x40
> >>>> [ 0.312847] get_page_from_freelist+0xa54/0x1310
> >>>> [ 0.312849] __alloc_frozen_pages_noprof+0x206/0x4c0
> >>>> [ 0.312851] ? __pfx___alloc_frozen_pages_noprof+0x10/0x10
> >>>> [ 0.312853] alloc_pages_mpol+0x13a/0x3f0
> >>>> [ 0.312855] ? __pfx_alloc_pages_mpol+0x10/0x10
> >>>> [ 0.312856] ? xas_find+0x2d8/0x450
> >>>> [ 0.312858] ? _raw_spin_lock+0x84/0xe0
> >>>> [ 0.312859] ? __pfx__raw_spin_lock+0x10/0x10
> >>>> [ 0.312861] alloc_pages_noprof+0xf6/0x2b0
> >>>> [ 0.312862] __change_page_attr+0x293/0x850
> >>>> [ 0.312864] ? __pfx___change_page_attr+0x10/0x10
> >>>> [ 0.312865] ? _vm_unmap_aliases+0x2d0/0x650
> >>>> [ 0.312868] ? __pfx__vm_unmap_aliases+0x10/0x10
> >>>> [ 0.312869] __change_page_attr_set_clr+0x16c/0x360
> >>>> [ 0.312871] ? spp_getpage+0xbb/0x1e0
> >>>> [ 0.312872] change_page_attr_set_clr+0x220/0x3c0
> >>>> [ 0.312873] ? flush_tlb_one_kernel+0xf/0x30
> >>>> [ 0.312875] ? set_pte_vaddr_p4d+0x110/0x180
> >>>> [ 0.312877] ? __pfx_change_page_attr_set_clr+0x10/0x10
> >>>> [ 0.312878] ? __pfx_set_pte_vaddr_p4d+0x10/0x10
> >>>> [ 0.312881] ? __pfx_mtree_load+0x10/0x10
> >>>> [ 0.312883] ? __pfx_mtree_load+0x10/0x10
> >>>> [ 0.312884] ? __asan_memcpy+0x3c/0x60
> >>>> [ 0.312886] ? set_intr_gate+0x10c/0x150
> >>>> [ 0.312888] set_memory_ro+0x76/0xa0
> >>>> [ 0.312889] ? __pfx_set_memory_ro+0x10/0x10
> >>>> [ 0.312891] idt_setup_apic_and_irq_gates+0x2c1/0x390
> >>>>
> >>>> and more.
> >>> Ok, it's not the only place. Got your point.
> >>>
> >>>> off topic - if we were to handle only alloc_page_ext() specifically,
> >>>> what would be the most straightforward
> >>>>
> >>>> solution in your mind? I'd really appreciate your insight.
> >>> I was thinking if it's the only special case maybe we can handle it
> >>> somehow differently, like we do when we allocate obj_ext vectors for
> >>> slabs using __GFP_NO_OBJ_EXT. I haven't found a good solution yet but
> >>> since it's not a special case we would not be able to use it even if I
> >>> came up with something...
> >>> I think your way is the most straight-forward but please try my
> >>> suggestion to see if we can avoid extra overhead.
> >>> Thanks,
> >>> Suren.
>
> Hi Suren
>
>
> > Hi Hao,
> >
> >> Hi Suren
> >>
> >> Thank you for your feedback. After re-examining this issue,
> >>
> >> I realize my previous focus was misplaced.
> >>
> >> Upon deeper consideration, I understand that this is not merely a bug,
> >>
> >> but rather a warning that indicates a gap in our memory profiling mechanism.
> >>
> >> Specifically, the current implementation appears to be missing memory
> >> allocation
> >>
> >> tracking during the period between the buddy system allocation and page_ext
> >>
> >> initialization.
> >>
> >> This profiling gap means we may not be capturing all relevant memory
> >> allocation
> >>
> >> events during this critical transition phase.
> > Correct, this limitation exists because memory profiling relies on
> > some kernel facilities (page_ext, objj_ext) which might not be
> > initialized yet at the time of allocation.
> >
> >> My approach is to dynamically allocate codetag_ref when get_page_tag_ref
> >> fails,
> >>
> >> and maintain a linked list to track all buddy system allocations that
> >> occur prior to page_ext initialization.
> >>
> >> However, this introduces performance concerns:
> >>
> >> 1. Free Path Overhead: When freeing these pages, we would need to
> >> traverse the entire linked list to locate
> >>
> >> the corresponding codetag_ref, resulting in O(n) lookup complexity
> >> per free operation.
> >>
> >> 2. Initialization Overhead: During init_page_alloc_tagging, iterating
> >> through the linked list to assign codetag_ref to
> >>
> >> page_ext would introduce additional traversal cost.
> >>
> >> If the number of pages is substantial, this could incur significant
> >> overhead. What are your thoughts on this? I look forward to your
> >> suggestions.
> > My thinking is that these early allocations comprise a small portion
> > of overall memory consumed by the system. So, instead of trying to
> > record and handle them in some alternative way, we just accept that
> > some counters might not be exactly accurate and ignore those early
> > allocations. See how the early slab allocations are marked with the
> > CODETAG_FLAG_INACCURATE flag and later reported as inaccurate. I think
> > that's an acceptable alternative to introducing extra complexity and
> > performance overhead. IOW, the benefits of accounting for these early
> > allocations are low compared to the effort required to account for
> > them. Unless you found a simple and performant way to do that...
>
>
> I have been exploring possible solutions to this issue over the past few
> days,
>
> but so far I have not come up with a good approach.
>
> I have counted the number of memory allocations that occur earlier than the
>
> allocation and initialization of our page_ext, and found that there are
> actually
>
> quite a lot of them.

Interesting... I wonder it's because deferred_struct_pages defers
page_ext initialization. Can you check if setting early_page_ext
reduces or eliminates these allocations before page_ext init cases?

>
> Similarly, I have made the following changes and collected the
> corresponding logs.
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 2d4b6f1a554e..6db65b3d52d3 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -1293,6 +1293,8 @@ void __pgalloc_tag_add(struct page *page, struct
> task_struct *task,
> alloc_tag_add(&ref, task->alloc_tag, PAGE_SIZE * nr);
> update_page_tag_ref(handle, &ref);
> put_page_tag_ref(handle);
> + } else{
> + pr_warn("__pgalloc_tag_add: get_page_tag_ref failed!
> page=%p pfn=%lu nr=%u\n", page, page_to_pfn(page), nr);
> }
> }
>
> @@ -1314,6 +1316,8 @@ void __pgalloc_tag_sub(struct page *page, unsigned
> int nr)
> alloc_tag_sub(&ref, PAGE_SIZE * nr);
> update_page_tag_ref(handle, &ref);
> put_page_tag_ref(handle);
> + } else{
> + pr_warn("__pgalloc_tag_sub: get_page_tag_ref failed!
> page=%p pfn=%lu nr=%u\n", page, page_to_pfn(page), nr);
> }
> }
>
> [ 0.261699] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004001000 pfn=1048640 nr=2
> [ 0.261711] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004001100 pfn=1048644 nr=4
> [ 0.261717] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004001200 pfn=1048648 nr=4
> [ 0.261721] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004001300 pfn=1048652 nr=4
> [ 0.261893] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004001080 pfn=1048642 nr=2
> [ 0.261917] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004001400 pfn=1048656 nr=4
> [ 0.262018] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004001500 pfn=1048660 nr=2
> [ 0.262024] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004001600 pfn=1048664 nr=8
> [ 0.262040] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004001580 pfn=1048662 nr=1
> [ 0.262048] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea00040015c0 pfn=1048663 nr=1
> [ 0.262056] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004001800 pfn=1048672 nr=2
> [ 0.262064] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004001880 pfn=1048674 nr=2
> [ 0.262078] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004001900 pfn=1048676 nr=2
> [ 0.262196] SLUB: HWalign=64, Order=0-3, MinObjects=0, CPUs=8, Nodes=1
> [ 0.262213] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004001980 pfn=1048678 nr=2
> [ 0.262220] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004001a00 pfn=1048680 nr=4
> [ 0.262246] ODEBUG: selftest passed
> [ 0.262268] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004001b00 pfn=1048684 nr=1
> [ 0.262318] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004001b40 pfn=1048685 nr=1
> [ 0.262368] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004001b80 pfn=1048686 nr=1
> [ 0.262418] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004001bc0 pfn=1048687 nr=1
> [ 0.262469] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004001c00 pfn=1048688 nr=1
> [ 0.262519] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004001c40 pfn=1048689 nr=1
> [ 0.262569] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004001c80 pfn=1048690 nr=1
> [ 0.262620] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004001cc0 pfn=1048691 nr=1
> [ 0.262670] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004001d00 pfn=1048692 nr=1
> [ 0.262721] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004001d40 pfn=1048693 nr=1
> [ 0.262771] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004001d80 pfn=1048694 nr=1
> [ 0.262821] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004001dc0 pfn=1048695 nr=1
> [ 0.262871] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004001e00 pfn=1048696 nr=1
> [ 0.262923] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004001e40 pfn=1048697 nr=1
> [ 0.262974] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004001e80 pfn=1048698 nr=1
> [ 0.263024] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004001ec0 pfn=1048699 nr=1
> [ 0.263074] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004001f00 pfn=1048700 nr=1
> [ 0.263124] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004001f40 pfn=1048701 nr=1
> [ 0.263174] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004001f80 pfn=1048702 nr=1
> [ 0.263224] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004001fc0 pfn=1048703 nr=1
> [ 0.263275] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004002000 pfn=1048704 nr=1
> [ 0.263325] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004002040 pfn=1048705 nr=1
> [ 0.263375] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004002080 pfn=1048706 nr=1
> [ 0.263427] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004002400 pfn=1048720 nr=16
> [ 0.263437] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea00040020c0 pfn=1048707 nr=1
> [ 0.263463] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004002100 pfn=1048708 nr=1
> [ 0.263465] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004002140 pfn=1048709 nr=1
> [ 0.263467] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004002180 pfn=1048710 nr=1
> [ 0.263509] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004002200 pfn=1048712 nr=4
> [ 0.263512] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004002800 pfn=1048736 nr=8
> [ 0.263524] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea00040021c0 pfn=1048711 nr=1
> [ 0.263536] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004002300 pfn=1048716 nr=1
> [ 0.263537] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004002340 pfn=1048717 nr=1
> [ 0.263539] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004002380 pfn=1048718 nr=1
> [ 0.263604] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004004000 pfn=1048832 nr=128
> [ 0.263638] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004003000 pfn=1048768 nr=64
> [ 0.263650] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004002c00 pfn=1048752 nr=16
> [ 0.263655] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea00040023c0 pfn=1048719 nr=1
> [ 0.270582] __pgalloc_tag_sub: get_page_tag_ref failed!
> page=ffffea00040023c0 pfn=1048719 nr=1
> [ 0.270591] ftrace: allocating 52717 entries in 208 pages
> [ 0.270592] ftrace: allocated 208 pages with 3 groups
> [ 0.270620] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004002a00 pfn=1048744 nr=8
> [ 0.270636] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea00040023c0 pfn=1048719 nr=1
> [ 0.270643] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004006000 pfn=1048960 nr=1
> [ 0.270649] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004006040 pfn=1048961 nr=1
> [ 0.270658] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004007000 pfn=1049024 nr=64
> [ 0.270659] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004006080 pfn=1048962 nr=2
> [ 0.270722] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004006100 pfn=1048964 nr=1
> [ 0.270730] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004006140 pfn=1048965 nr=1
> [ 0.270738] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004006180 pfn=1048966 nr=1
> [ 0.270777] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea00040061c0 pfn=1048967 nr=1
> [ 0.270786] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004006200 pfn=1048968 nr=1
> [ 0.270792] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004006240 pfn=1048969 nr=1
> [ 0.270833] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004006300 pfn=1048972 nr=4
> [ 0.270891] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004006280 pfn=1048970 nr=1
> [ 0.270980] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea00040062c0 pfn=1048971 nr=1
> [ 0.271071] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004006400 pfn=1048976 nr=1
> [ 0.271156] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004006440 pfn=1048977 nr=1
> [ 0.271185] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004006480 pfn=1048978 nr=2
> [ 0.271301] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004006500 pfn=1048980 nr=1
> [ 0.271655] Dynamic Preempt: lazy
> [ 0.271662] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004006580 pfn=1048982 nr=2
> [ 0.271752] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004006600 pfn=1048984 nr=4
> [ 0.271762] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004010000 pfn=1049600 nr=4
> [ 0.271824] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004006540 pfn=1048981 nr=1
> [ 0.271916] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004006700 pfn=1048988 nr=2
> [ 0.271964] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004006780 pfn=1048990 nr=1
> [ 0.272099] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea00040067c0 pfn=1048991 nr=1
> [ 0.272138] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004006800 pfn=1048992 nr=2
> [ 0.272144] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004006a00 pfn=1049000 nr=8
> [ 0.272249] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004006c00 pfn=1049008 nr=8
> [ 0.272319] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004006880 pfn=1048994 nr=2
> [ 0.272351] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004006900 pfn=1048996 nr=4
> [ 0.272424] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004006e00 pfn=1049016 nr=8
> [ 0.272485] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004008000 pfn=1049088 nr=8
> [ 0.272535] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004008200 pfn=1049096 nr=2
> [ 0.272600] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004008400 pfn=1049104 nr=8
> [ 0.272663] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004008300 pfn=1049100 nr=4
> [ 0.272694] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004008280 pfn=1049098 nr=2
> [ 0.272708] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004008600 pfn=1049112 nr=8
>
> [ 0.272924] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004008880 pfn=1049122 nr=2
> [ 0.272934] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004008900 pfn=1049124 nr=2
> [ 0.272952] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004008c00 pfn=1049136 nr=4
> [ 0.273035] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004008980 pfn=1049126 nr=2
> [ 0.273062] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004008e00 pfn=1049144 nr=8
> [ 0.273674] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004008d00 pfn=1049140 nr=1
> [ 0.273884] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004008d80 pfn=1049142 nr=2
> [ 0.273943] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004009000 pfn=1049152 nr=2
> [ 0.274379] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004009080 pfn=1049154 nr=2
> [ 0.274575] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004009200 pfn=1049160 nr=8
> [ 0.274617] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004009100 pfn=1049156 nr=4
> [ 0.274794] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004009400 pfn=1049168 nr=2
> [ 0.274840] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004009480 pfn=1049170 nr=2
> [ 0.275057] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004009500 pfn=1049172 nr=2
> [ 0.275092] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004009580 pfn=1049174 nr=2
> [ 0.275134] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004009600 pfn=1049176 nr=8
> [ 0.275211] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004009800 pfn=1049184 nr=4
> [ 0.275510] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004009900 pfn=1049188 nr=2
> [ 0.275548] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004009980 pfn=1049190 nr=2
> [ 0.275976] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004009a00 pfn=1049192 nr=8
> [ 0.275987] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004009c00 pfn=1049200 nr=2
> [ 0.276139] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004009c80 pfn=1049202 nr=2
> [ 0.276152] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004008d40 pfn=1049141 nr=1
> [ 0.276242] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004009d00 pfn=1049204 nr=1
> [ 0.276358] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004009d40 pfn=1049205 nr=1
> [ 0.276444] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004009d80 pfn=1049206 nr=1
> [ 0.276526] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004009dc0 pfn=1049207 nr=1
> [ 0.276615] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004009e00 pfn=1049208 nr=1
> [ 0.276696] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004009e40 pfn=1049209 nr=1
> [ 0.276792] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004009e80 pfn=1049210 nr=1
> [ 0.276827] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004009f00 pfn=1049212 nr=2
> [ 0.276891] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004009ec0 pfn=1049211 nr=1
> [ 0.276999] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004009f80 pfn=1049214 nr=1
> [ 0.277082] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea0004009fc0 pfn=1049215 nr=1
> [ 0.277172] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea000400a000 pfn=1049216 nr=1
> [ 0.277257] __pgalloc_tag_add: get_page_tag_ref failed!
> page=ffffea000400a040 pfn=1049217 nr=1
>
> and so on.
>
>
> > I think your earlier patch can effectively detect these early
> > allocations and suppress the warnings. We should also mark these
> > allocations with CODETAG_FLAG_INACCURATE.
>
> Thanks to an excellent AI review, I realized there are issues with
>
> my original patch. One problem is the 256-element array; another

Yes, if there are lots of such allocations, it's not appropriate.

>
> is that it involves allocation and free operations — meaning we need
>
> to record entries at __pgalloc_tag_add and remove them at __pgalloc_tag_sub,
>
> which introduces a noticeable overhead. I'm wondering if we can instead
> set a flag
>
> bit in page flags during the early boot stage, which I'll refer to as
> EARLY_ALLOC_FLAGS.
>
> Then, in __pgalloc_tag_sub, we first check for EARLY_ALLOC_FLAGS. If
> set, we clear the
>
> flag and return immediately; otherwise, we perform the actual
> subtraction of the tag count.
>
> This approach seems somewhat similar to the idea behind
> mem_profiling_compressed.

That seems doable but let's first check if we can make page_ext
initialization happen before these allocations. That would be the
ideal path. If it's not possible then we can focus on alternatives
like the one you propose.

>
> I would appreciate your valuable feedback and any better suggestions you
> might have.

Thanks for pursuing this! I'll help in any way I can.
Suren.

>
> Thanks
>
> Hao
>
> > Thanks,
> > Suren.
> >
> >>
> >> Thanks
> >>
> >> Hao
> >>
> >>>> Thanks.
> >>>>
> >>>>
> >>>>>>>> If the slab cache has no free objects, it falls back
> >>>>>>>> to the buddy allocator to allocate memory. However, at this point page_ext
> >>>>>>>> is not yet fully initialized, so these newly allocated pages have no
> >>>>>>>> codetag set. These pages may later be reclaimed by KASAN,which causes
> >>>>>>>> the warning to trigger when they are freed because their codetag ref is
> >>>>>>>> still empty.
> >>>>>>>>
> >>>>>>>> Use a global array to track pages allocated before page_ext is fully
> >>>>>>>> initialized, similar to how kmemleak tracks early allocations.
> >>>>>>>> When page_ext initialization completes, set their codetag
> >>>>>>>> to empty to avoid warnings when they are freed later.
> >>>>>>>>
> >>>>>>>> ...
> >>>>>>>>
> >>>>>>>> --- a/include/linux/alloc_tag.h
> >>>>>>>> +++ b/include/linux/alloc_tag.h
> >>>>>>>> @@ -74,6 +74,9 @@ static inline void set_codetag_empty(union codetag_ref *ref)
> >>>>>>>>
> >>>>>>>> #ifdef CONFIG_MEM_ALLOC_PROFILING
> >>>>>>>>
> >>>>>>>> +bool mem_profiling_is_available(void);
> >>>>>>>> +void alloc_tag_add_early_pfn(unsigned long pfn);
> >>>>>>>> +
> >>>>>>>> #define ALLOC_TAG_SECTION_NAME "alloc_tags"
> >>>>>>>>
> >>>>>>>> struct codetag_bytes {
> >>>>>>>> diff --git a/lib/alloc_tag.c b/lib/alloc_tag.c
> >>>>>>>> index 58991ab09d84..a5bf4e72c154 100644
> >>>>>>>> --- a/lib/alloc_tag.c
> >>>>>>>> +++ b/lib/alloc_tag.c
> >>>>>>>> @@ -6,6 +6,7 @@
> >>>>>>>> #include <linux/kallsyms.h>
> >>>>>>>> #include <linux/module.h>
> >>>>>>>> #include <linux/page_ext.h>
> >>>>>>>> +#include <linux/pgalloc_tag.h>
> >>>>>>>> #include <linux/proc_fs.h>
> >>>>>>>> #include <linux/seq_buf.h>
> >>>>>>>> #include <linux/seq_file.h>
> >>>>>>>> @@ -26,6 +27,82 @@ static bool mem_profiling_support;
> >>>>>>>>
> >>>>>>>> static struct codetag_type *alloc_tag_cttype;
> >>>>>>>>
> >>>>>>>> +/*
> >>>>>>>> + * State of the alloc_tag
> >>>>>>>> + *
> >>>>>>>> + * This is used to describe the states of the alloc_tag during bootup.
> >>>>>>>> + *
> >>>>>>>> + * When we need to allocate page_ext to store codetag, we face an
> >>>>>>>> + * initialization timing problem:
> >>>>>>>> + *
> >>>>>>>> + * Due to initialization order, pages may be allocated via buddy system
> >>>>>>>> + * before page_ext is fully allocated and initialized. Although these
> >>>>>>>> + * pages call the allocation hooks, the codetag will not be set because
> >>>>>>>> + * page_ext is not yet available.
> >>>>>>>> + *
> >>>>>>>> + * When these pages are later free to the buddy system, it triggers
> >>>>>>>> + * warnings because their codetag is actually empty if
> >>>>>>>> + * CONFIG_MEM_ALLOC_PROFILING_DEBUG is enabled.
> >>>>>>>> + *
> >>>>>>>> + * Additionally, in this situation, we cannot record detailed allocation
> >>>>>>>> + * information for these pages.
> >>>>>>>> + */
> >>>>>>>> +enum mem_profiling_state {
> >>>>>>>> + DOWN, /* No mem_profiling functionality yet */
> >>>>>>>> + UP /* Everything is working */
> >>>>>>>> +};
> >>>>>>>> +
> >>>>>>>> +static enum mem_profiling_state mem_profiling_state = DOWN;
> >>>>>>>> +
> >>>>>>>> +bool mem_profiling_is_available(void)
> >>>>>>>> +{
> >>>>>>>> + return mem_profiling_state == UP;
> >>>>>>>> +}
> >>>>>>>> +
> >>>>>>>> +#ifdef CONFIG_MEM_ALLOC_PROFILING_DEBUG
> >>>>>>>> +
> >>>>>>>> +#define EARLY_ALLOC_PFN_MAX 256
> >>>>>>>> +
> >>>>>>>> +static unsigned long early_pfns[EARLY_ALLOC_PFN_MAX];
> >>>>>>> It's unfortunate that this isn't __initdata.
> >>>>>>>
> >>>>>>>> +static unsigned int early_pfn_count;
> >>>>>>>> +static DEFINE_SPINLOCK(early_pfn_lock);
> >>>>>>>> +
> >>>>>>>>
> >>>>>>>> ...
> >>>>>>>>
> >>>>>>>> --- a/mm/page_alloc.c
> >>>>>>>> +++ b/mm/page_alloc.c
> >>>>>>>> @@ -1293,6 +1293,13 @@ void __pgalloc_tag_add(struct page *page, struct task_struct *task,
> >>>>>>>> alloc_tag_add(&ref, task->alloc_tag, PAGE_SIZE * nr);
> >>>>>>>> update_page_tag_ref(handle, &ref);
> >>>>>>>> put_page_tag_ref(handle);
> >>>>>>>> + } else {
> >>>>>> This branch can be marked as "unlikely".
> >>>>>>
> >>>>>>>> + /*
> >>>>>>>> + * page_ext is not available yet, record the pfn so we can
> >>>>>>>> + * clear the tag ref later when page_ext is initialized.
> >>>>>>>> + */
> >>>>>>>> + if (!mem_profiling_is_available())
> >>>>>>>> + alloc_tag_add_early_pfn(page_to_pfn(page));
> >>>>>>>> }
> >>>>>>>> }
> >>>>>>> All because of this, I believe. Is this fixable?
> >>>>>>>
> >>>>>>> If we take that `else', we know we're running in __init code, yes? I
> >>>>>>> don't see how `__init pgalloc_tag_add_early()' could be made to work.
> >>>>>>> hrm. Something clever, please.
> >>>>>> We can have a pointer to a function that is initialized to point to
> >>>>>> alloc_tag_add_early_pfn, which is defined as __init and uses
> >>>>>> early_pfns which now can be defined as __initdata. After
> >>>>>> clear_early_alloc_pfn_tag_refs() is done we reset that pointer to
> >>>>>> NULL. __pgalloc_tag_add() instead of calling alloc_tag_add_early_pfn()
> >>>>>> directly checks that pointer and if it's not NULL then calls the
> >>>>>> function that it points to. This way __pgalloc_tag_add() which is not
> >>>>>> an __init function will be invoking alloc_tag_add_early_pfn() __init
> >>>>>> function only until we are done with initialization. I haven't tried
> >>>>>> this but I think that should work. This also eliminates the need for
> >>>>>> mem_profiling_state variable since we can use this function pointer
> >>>>>> instead.
> >>>>>>
> >>>>>>