Re: [PATCH V2 0/6] mm: page_alloc: freelist migratetype hygiene

[Zi Yan]

On 19 Sep 2023, at 14:47, Mike Kravetz wrote:

> On 09/19/23 02:49, Johannes Weiner wrote:
>> On Mon, Sep 18, 2023 at 10:40:37AM -0700, Mike Kravetz wrote:
>>> On 09/18/23 10:52, Johannes Weiner wrote:
>>>> On Mon, Sep 18, 2023 at 09:16:58AM +0200, Vlastimil Babka wrote:
>>>>> On 9/16/23 21:57, Mike Kravetz wrote:
>>>>>> On 09/15/23 10:16, Johannes Weiner wrote:
>>>>>>> On Thu, Sep 14, 2023 at 04:52:38PM -0700, Mike Kravetz wrote:
>>>>>>
>>>>>> With the patch below applied, a slightly different workload triggers the
>>>>>> following warnings.  It seems related, and appears to go away when
>>>>>> reverting the series.
>>>>>>
>>>>>> [  331.595382] ------------[ cut here ]------------
>>>>>> [  331.596665] page type is 5, passed migratetype is 1 (nr=512)
>>>>>> [  331.598121] WARNING: CPU: 2 PID: 935 at mm/page_alloc.c:662 expand+0x1c9/0x200
>>>>>
>>>>> Initially I thought this demonstrates the possible race I was suggesting in
>>>>> reply to 6/6. But, assuming you have CONFIG_CMA, page type 5 is cma and we
>>>>> are trying to get a MOVABLE page from a CMA page block, which is something
>>>>> that's normally done and the pageblock stays CMA. So yeah if the warnings
>>>>> are to stay, they need to handle this case. Maybe the same can happen with
>>>>> HIGHATOMIC blocks?
>>
>> Ok, the CMA thing gave me pause because Mike's pagetypeinfo didn't
>> show any CMA pages.
>>
>> 5 is actually MIGRATE_ISOLATE - see the double use of 3 for PCPTYPES
>> and HIGHATOMIC.
>>
>>>> This means we have an order-10 page where one half is MOVABLE and the
>>>> other is CMA.
>>
>> This means the scenario is different:
>>
>> We get a MAX_ORDER page off the MOVABLE freelist. The removal checks
>> that the first pageblock is indeed MOVABLE. During the expand, the
>> second pageblock turns out to be of type MIGRATE_ISOLATE.
>>
>> The page allocator wouldn't have merged those types. It triggers a bit
>> too fast to be a race condition.
>>
>> It appears that MIGRATE_ISOLATE is simply set on the tail pageblock
>> while the head is on the list, and then stranded there.
>>
>> Could this be an issue in the page_isolation code? Maybe a range
>> rounding error?
>>
>> Zi Yan, does this ring a bell for you?
>>
>> I don't quite see how my patches could have caused this. But AFAICS we
>> also didn't have warnings for this scenario so it could be an old bug.
>>
>>>> Mike, could you describe the workload that is triggering this?
>>>
>>> This 'slightly different workload' is actually a slightly different
>>> environment.  Sorry for mis-speaking!  The slight difference is that this
>>> environment does not use the 'alloc hugetlb gigantic pages from CMA'
>>> (hugetlb_cma) feature that triggered the previous issue.
>>>
>>> This is still on a 16G VM.  Kernel command line here is:
>>> "BOOT_IMAGE=(hd0,msdos1)/vmlinuz-6.6.0-rc1-next-20230913+
>>> root=UUID=49c13301-2555-44dc-847b-caabe1d62bdf ro console=tty0
>>> console=ttyS0,115200 audit=0 selinux=0 transparent_hugepage=always
>>> hugetlb_free_vmemmap=on"
>>>
>>> The workload is just running this script:
>>> while true; do
>>>  echo 4 > /sys/kernel/mm/hugepages/hugepages-1048576kB/nr_hugepages
>>>  echo 4 > /sys/kernel/mm/hugepages/hugepages-1048576kB/demote
>>>  echo 0 > /sys/kernel/mm/hugepages/hugepages-2048kB/nr_hugepages
>>> done
>>>
>>>>
>>>> Does this reproduce instantly and reliably?
>>>>
>>>
>>> It is not 'instant' but will reproduce fairly reliably within a minute
>>> or so.
>>>
>>> Note that the 'echo 4 > .../hugepages-1048576kB/nr_hugepages' is going
>>> to end up calling alloc_contig_pages -> alloc_contig_range.  Those pages
>>> will eventually be freed via __free_pages(folio, 9).
>>
>> No luck reproducing this yet, but I have a question. In that crash
>> stack trace, the expand() is called via this:
>>
>>  [  331.645847]  get_page_from_freelist+0x3ed/0x1040
>>  [  331.646837]  ? prepare_alloc_pages.constprop.0+0x197/0x1b0
>>  [  331.647977]  __alloc_pages+0xec/0x240
>>  [  331.648783]  alloc_buddy_hugetlb_folio.isra.0+0x6a/0x150
>>  [  331.649912]  __alloc_fresh_hugetlb_folio+0x157/0x230
>>  [  331.650938]  alloc_pool_huge_folio+0xad/0x110
>>  [  331.651909]  set_max_huge_pages+0x17d/0x390
>>
>> I don't see an __alloc_fresh_hugetlb_folio() in my tree. Only
>> alloc_fresh_hugetlb_folio(), which has this:
>>
>>         if (hstate_is_gigantic(h))
>>                 folio = alloc_gigantic_folio(h, gfp_mask, nid, nmask);
>>         else
>>                 folio = alloc_buddy_hugetlb_folio(h, gfp_mask,
>>                                 nid, nmask, node_alloc_noretry);
>>
>> where gigantic is defined as the order exceeding MAX_ORDER, which
>> should be the case for 1G pages on x86.
>>
>> So the crashing stack must be from a 2M allocation, no? I'm confused
>> how that could happen with the above test case.
>
> Sorry for causing the confusion!
>
> When I originally saw the warnings pop up, I was running the above script
> as well as another that only allocated order 9 hugetlb pages:
>
> while true; do
> 	echo 2048 > /sys/kernel/mm/hugepages/hugepages-2048kB/nr_hugepages
> 	echo 0 > /sys/kernel/mm/hugepages/hugepages-2048kB/nr_hugepages
> done
>
> The warnings were actually triggered by allocations in this second script.
>
> However, when reporting the warnings I wanted to include the simplest
> way to recreate.  And, I noticed that that second script running in
> parallel was not required.  Again, sorry for the confusion!  Here is a
> warning triggered via the alloc_contig_range path only running the one
> script.
>
> [  107.275821] ------------[ cut here ]------------
> [  107.277001] page type is 0, passed migratetype is 1 (nr=512)
> [  107.278379] WARNING: CPU: 1 PID: 886 at mm/page_alloc.c:699 del_page_from_free_list+0x137/0x170
> [  107.280514] Modules linked in: rfkill ip6table_filter ip6_tables sunrpc snd_hda_codec_generic joydev 9p snd_hda_intel netfs snd_intel_dspcfg snd_hda_codec snd_hwdep 9pnet_virtio snd_hda_core snd_seq snd_seq_device 9pnet virtio_balloon snd_pcm snd_timer snd soundcore virtio_net net_failover failover virtio_console virtio_blk crct10dif_pclmul crc32_pclmul crc32c_intel ghash_clmulni_intel serio_raw virtio_pci virtio virtio_pci_legacy_dev virtio_pci_modern_dev virtio_ring fuse
> [  107.291033] CPU: 1 PID: 886 Comm: bash Not tainted 6.6.0-rc2-next-20230919-dirty #35
> [  107.293000] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-1.fc37 04/01/2014
> [  107.295187] RIP: 0010:del_page_from_free_list+0x137/0x170
> [  107.296618] Code: c6 05 20 9b 35 01 01 e8 b7 fb ff ff 44 89 f1 44 89 e2 48 c7 c7 d8 ab 22 82 48 89 c6 b8 01 00 00 00 d3 e0 89 c1 e8 e9 99 df ff <0f> 0b e9 03 ff ff ff 48 c7 c6 10 ac 22 82 48 89 df e8 f3 e0 fc ff
> [  107.301236] RSP: 0018:ffffc90003ba7a70 EFLAGS: 00010086
> [  107.302535] RAX: 0000000000000000 RBX: ffffea0007ff8000 RCX: 0000000000000000
> [  107.304467] RDX: 0000000000000004 RSI: ffffffff8224e9de RDI: 00000000ffffffff
> [  107.306289] RBP: 00000000001ffe00 R08: 0000000000009ffb R09: 00000000ffffdfff
> [  107.308135] R10: 00000000ffffdfff R11: ffffffff824660e0 R12: 0000000000000001
> [  107.309956] R13: ffff88827fffcd80 R14: 0000000000000009 R15: 00000000001ffc00
> [  107.311839] FS:  00007fabb8cba740(0000) GS:ffff888277d00000(0000) knlGS:0000000000000000
> [  107.314695] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [  107.316159] CR2: 00007f41ba01acf0 CR3: 0000000282ed4006 CR4: 0000000000370ee0
> [  107.317971] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> [  107.319783] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> [  107.321575] Call Trace:
> [  107.322314]  <TASK>
> [  107.323002]  ? del_page_from_free_list+0x137/0x170
> [  107.324380]  ? __warn+0x7d/0x130
> [  107.325341]  ? del_page_from_free_list+0x137/0x170
> [  107.326627]  ? report_bug+0x18d/0x1c0
> [  107.327632]  ? prb_read_valid+0x17/0x20
> [  107.328711]  ? handle_bug+0x41/0x70
> [  107.329685]  ? exc_invalid_op+0x13/0x60
> [  107.330787]  ? asm_exc_invalid_op+0x16/0x20
> [  107.331937]  ? del_page_from_free_list+0x137/0x170
> [  107.333189]  __free_one_page+0x2ab/0x6f0
> [  107.334375]  free_pcppages_bulk+0x169/0x210
> [  107.335575]  drain_pages_zone+0x3f/0x50
> [  107.336691]  __drain_all_pages+0xe2/0x1e0
> [  107.337843]  alloc_contig_range+0x143/0x280
> [  107.339026]  alloc_contig_pages+0x210/0x270
> [  107.340200]  alloc_fresh_hugetlb_folio+0xa6/0x270
> [  107.341529]  alloc_pool_huge_page+0x7d/0x100
> [  107.342745]  set_max_huge_pages+0x162/0x340
> [  107.345059]  nr_hugepages_store_common+0x91/0xf0
> [  107.346329]  kernfs_fop_write_iter+0x108/0x1f0
> [  107.347547]  vfs_write+0x207/0x400
> [  107.348543]  ksys_write+0x63/0xe0
> [  107.349511]  do_syscall_64+0x37/0x90
> [  107.350543]  entry_SYSCALL_64_after_hwframe+0x6e/0xd8
> [  107.351940] RIP: 0033:0x7fabb8daee87
> [  107.352819] Code: 0d 00 f7 d8 64 89 02 48 c7 c0 ff ff ff ff eb b7 0f 1f 00 f3 0f 1e fa 64 8b 04 25 18 00 00 00 85 c0 75 10 b8 01 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 51 c3 48 83 ec 28 48 89 54 24 18 48 89 74 24
> [  107.356373] RSP: 002b:00007ffc02737478 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
> [  107.358103] RAX: ffffffffffffffda RBX: 0000000000000002 RCX: 00007fabb8daee87
> [  107.359695] RDX: 0000000000000002 RSI: 000055fe584a1620 RDI: 0000000000000001
> [  107.361258] RBP: 000055fe584a1620 R08: 000000000000000a R09: 00007fabb8e460c0
> [  107.362842] R10: 00007fabb8e45fc0 R11: 0000000000000246 R12: 0000000000000002
> [  107.364385] R13: 00007fabb8e82520 R14: 0000000000000002 R15: 00007fabb8e82720
> [  107.365968]  </TASK>
> [  107.366534] ---[ end trace 0000000000000000 ]---
> [  121.542474] ------------[ cut here ]------------
>
> Perhaps that is another piece of information in that the warning can be
> triggered via both allocation paths.
>
> To be perfectly clear, here is what I did today:
> - built next-20230919.  It does not contain your series
>   	I could not recreate the issue.
> - Added your series and the patch to remove
>   VM_BUG_ON_PAGE(is_migrate_isolate(mt), page) from free_pcppages_bulk
> 	I could recreate the issue while running only the one script.
> 	The warning above is from that run.
> - Added this suggested patch from Zi
> 	diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> 	index 1400e674ab86..77a4aea31a7f 100644
> 	--- a/mm/page_alloc.c
> 	+++ b/mm/page_alloc.c
> 	@@ -1651,8 +1651,13 @@ static bool prep_move_freepages_block(struct zone *zone, struct page *page,
>  		end = pageblock_end_pfn(pfn) - 1;
>
>  		/* Do not cross zone boundaries */
> 	+#if 0
>  		if (!zone_spans_pfn(zone, start))
> 			start = zone->zone_start_pfn;
> 	+#else
> 	+	if (!zone_spans_pfn(zone, start))
> 	+		start = pfn;
> 	+#endif
> 	 	if (!zone_spans_pfn(zone, end))
> 	 		return false;
> 	I can still trigger warnings.

OK. One thing to note is that the page type in the warning changed from
5 (MIGRATE_ISOLATE) to 0 (MIGRATE_UNMOVABLE) with my suggested change.

>
> One idea about recreating the issue is that it may have to do with size
> of my VM (16G) and the requested allocation sizes 4G.  However, I tried
> to really stress the allocations by increasing the number of hugetlb
> pages requested and that did not help.  I also noticed that I only seem
> to get two warnings and then they stop, even if I continue to run the
> script.
>
> Zi asked about my config, so it is attached.

With your config, I still have no luck reproducing the issue. I will keep
trying. Thanks.


--
Best Regards,
Yan, Zi

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