linux-kernel - Re: [PATCH v2 00/17] mm: fixes for device-exclusive entries (hmm)

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Message-ID: <CAGsJ_4yVkJdKejof1CxJY1hkUSsQ-ziRzCTp9CBXdBJ-4d1HHw@mail.gmail.com>
Date: Tue, 11 Feb 2025 12:39:07 +1300
From: Barry Song <21cnbao@...il.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: David Hildenbrand <david@...hat.com>, linux-kernel@...r.kernel.org, 
	linux-doc@...r.kernel.org, dri-devel@...ts.freedesktop.org, 
	linux-mm@...ck.org, nouveau@...ts.freedesktop.org, 
	linux-trace-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org, 
	damon@...ts.linux.dev, Jérôme Glisse <jglisse@...hat.com>, 
	Jonathan Corbet <corbet@....net>, Alex Shi <alexs@...nel.org>, Yanteng Si <si.yanteng@...ux.dev>, 
	Karol Herbst <kherbst@...hat.com>, Lyude Paul <lyude@...hat.com>, 
	Danilo Krummrich <dakr@...nel.org>, David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>, 
	Masami Hiramatsu <mhiramat@...nel.org>, Oleg Nesterov <oleg@...hat.com>, 
	Peter Zijlstra <peterz@...radead.org>, SeongJae Park <sj@...nel.org>, 
	"Liam R. Howlett" <Liam.Howlett@...cle.com>, Lorenzo Stoakes <lorenzo.stoakes@...cle.com>, 
	Vlastimil Babka <vbabka@...e.cz>, Jann Horn <jannh@...gle.com>, 
	Pasha Tatashin <pasha.tatashin@...een.com>, Peter Xu <peterx@...hat.com>, 
	Alistair Popple <apopple@...dia.com>, Jason Gunthorpe <jgg@...dia.com>, Barry Song <v-songbaohua@...o.com>
Subject: Re: [PATCH v2 00/17] mm: fixes for device-exclusive entries (hmm)

On Tue, Feb 11, 2025 at 12:05 PM Andrew Morton
<akpm@...ux-foundation.org> wrote:
>
> On Mon, 10 Feb 2025 20:37:42 +0100 David Hildenbrand <david@...hat.com> wrote:
>
> > Against mm-hotfixes-stable for now.
> >
> > Discussing the PageTail() call in make_device_exclusive_range() with
> > Willy, I recently discovered [1] that device-exclusive handling does
> > not properly work with THP, making the hmm-tests selftests fail if THPs
> > are enabled on the system.
> >
> > Looking into more details, I found that hugetlb is not properly fenced,
> > and I realized that something that was bugging me for longer -- how
> > device-exclusive entries interact with mapcounts -- completely breaks
> > migration/swapout/split/hwpoison handling of these folios while they have
> > device-exclusive PTEs.
> >
> > The program below can be used to allocate 1 GiB worth of pages and
> > making them device-exclusive on a kernel with CONFIG_TEST_HMM.
> >
> > Once they are device-exclusive, these folios cannot get swapped out
> > (proc$pid/smaps_rollup will always indicate 1 GiB RSS no matter how
> > much one forces memory reclaim), and when having a memory block onlined
> > to ZONE_MOVABLE, trying to offline it will loop forever and complain about
> > failed migration of a page that should be movable.
> >
> > # echo offline > /sys/devices/system/memory/memory136/state
> > # echo online_movable > /sys/devices/system/memory/memory136/state
> > # ./hmm-swap &
> > ... wait until everything is device-exclusive
> > # echo offline > /sys/devices/system/memory/memory136/state
> > [  285.193431][T14882] page: refcount:2 mapcount:0 mapping:0000000000000000
> >   index:0x7f20671f7 pfn:0x442b6a
> > [  285.196618][T14882] memcg:ffff888179298000
> > [  285.198085][T14882] anon flags: 0x5fff0000002091c(referenced|uptodate|
> >   dirty|active|owner_2|swapbacked|node=1|zone=3|lastcpupid=0x7ff)
> > [  285.201734][T14882] raw: ...
> > [  285.204464][T14882] raw: ...
> > [  285.207196][T14882] page dumped because: migration failure
> > [  285.209072][T14882] page_owner tracks the page as allocated
> > [  285.210915][T14882] page last allocated via order 0, migratetype
> >   Movable, gfp_mask 0x140dca(GFP_HIGHUSER_MOVABLE|__GFP_COMP|__GFP_ZERO),
> >   id 14926, tgid 14926 (hmm-swap), ts 254506295376, free_ts 227402023774
> > [  285.216765][T14882]  post_alloc_hook+0x197/0x1b0
> > [  285.218874][T14882]  get_page_from_freelist+0x76e/0x3280
> > [  285.220864][T14882]  __alloc_frozen_pages_noprof+0x38e/0x2740
> > [  285.223302][T14882]  alloc_pages_mpol+0x1fc/0x540
> > [  285.225130][T14882]  folio_alloc_mpol_noprof+0x36/0x340
> > [  285.227222][T14882]  vma_alloc_folio_noprof+0xee/0x1a0
> > [  285.229074][T14882]  __handle_mm_fault+0x2b38/0x56a0
> > [  285.230822][T14882]  handle_mm_fault+0x368/0x9f0
> > ...
> >
> > This series fixes all issues I found so far.
>
> Cool.
>
> Barry, could you please redo your series "mm: batched unmap lazyfree
> large folios during reclamation" on top of this (on top of mm-unstable,
> ideally).

Sure. Thanks for letting me know.

>