From: Zi Yan <ziy@nvidia.com>
To: "David Hildenbrand (Arm)" <david@kernel.org>
Cc: Usama Arif <usama.arif@linux.dev>,
Andrew Morton <akpm@linux-foundation.org>,
chrisl@kernel.org, kasong@tencent.com, ljs@kernel.org,
linux-mm@kvack.org, ying.huang@linux.alibaba.com,
Baoquan He <baoquan.he@linux.dev>,
willy@infradead.org, youngjun.park@lge.com, hannes@cmpxchg.org,
riel@surriel.com, shakeel.butt@linux.dev, alex@ghiti.fr,
kas@kernel.org, baohua@kernel.org, dev.jain@arm.com,
baolin.wang@linux.alibaba.com, Nico Pache <nico.pache@linux.dev>,
"Liam R. Howlett" <liam@infradead.org>,
ryan.roberts@arm.com, Vlastimil Babka <vbabka@kernel.org>,
lance.yang@linux.dev, linux-kernel@vger.kernel.org,
nphamcs@gmail.com, shikemeng@huaweicloud.com, yosry@kernel.org,
qi.zheng@linux.dev, luizcap@redhat.com, kernel-team@meta.com
Subject: Re: [PATCH v8 00/30] mm: PMD-level swap entries for anonymous THPs
Date: Fri, 02 Oct 2026 11:13:55 -0400 [thread overview]
Message-ID: <D596001F-875E-4061-8124-68B0DB34CF19@nvidia.com> (raw)
In-Reply-To: <ebc72eb7-daf3-45be-8994-b51e5e301b56@kernel.org>
On 2 Oct 2026, at 10:28, David Hildenbrand (Arm) wrote:
> On 10/2/26 11:52, Usama Arif wrote:
>> When reclaim swaps out a PMD-mapped anonymous THP today, the PMD is
>> split into HPAGE_PMD_NR PTE-level swap entries via TTU_SPLIT_HUGE_PMD
>> before unmap. This series introduces a PMD-level swap entry so the
>> huge mapping can survive the swap round-trip and do_huge_pmd_swap_page()
>> can restore the PMD mapping directly on swap-in, without waiting for
>> khugepaged to collapse the range later.
>>
>> The PMD swap entry is a compact page-table encoding for HPAGE_PMD_NR
>> consecutive swap slots. swap_map accounting remains per-slot and is
>> unchanged. Importantly, a PMD swap entry does not promise that the swap
>> cache always contains one PMD-sized folio. While the cache is empty or
>> contains one PMD-sized folio, PMD-level handling can proceed. Once the
>> cache has split/per-slot state, users either inspect the individual
>> slots directly (mincore) or split the PMD swap entry and retry through
>> the PTE path (fault, swapoff, MADV_WILLNEED, UFFDIO_MOVE). MADV_FREE
>> does not consult the cache at all: it frees a whole PMD swap entry in
>> place and only splits when the advised range covers part of the PMD.
>> Likewise, if any slot is still backed by zswap's per-page
>> store, PMD-order swap-in consumers split and let the PTE path load the
>> range page by page; an all-on-disk range can still be read back as one
>> PMD-sized folio.
>>
>> The series is ordered so every consumer can handle PMD swap entries
>> before the swap-out producer starts installing them. The swap-out patch
>> is the last functional change.
>>
<snip>
>
> I was hoping that we could get this into the next merge window, but as we are
> approach rc6 and I didn't even manage to review all patches (shame on me), I
> assume this would be a quite fit.
>
> So I assume this series is one of the things that we'll try to get in shape over
> the next merge window to queue it early after rc1.
I am going to review this series, since I have done with Lorenzo’s VM_SPECIAL one.
Best Regards,
Yan, Zi
prev parent reply other threads:[~2026-10-02 15:14 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-10-02 9:52 Usama Arif
2026-10-02 9:52 ` [PATCH v8 01/30] mm: rename pmd_to_softleaf_folio() to pmd_softleaf_to_folio() Usama Arif
2026-10-02 9:52 ` [PATCH v8 02/30] arm64: mm: add PMD swap-exclusive helpers Usama Arif
2026-10-02 9:52 ` [PATCH v8 03/30] loongarch: " Usama Arif
2026-10-02 14:17 ` Huacai Chen
2026-10-02 9:52 ` [PATCH v8 04/30] powerpc: " Usama Arif
2026-10-02 9:52 ` [PATCH v8 05/30] riscv: " Usama Arif
2026-10-02 9:52 ` [PATCH v8 06/30] s390: " Usama Arif
2026-10-02 9:52 ` [PATCH v8 07/30] x86: " Usama Arif
2026-10-02 9:52 ` [PATCH v8 08/30] mm: recognize PMD swap entries in the softleaf layer Usama Arif
2026-10-02 9:52 ` [PATCH v8 09/30] mm/debug_vm_pgtable: test PMD swap-exclusive helpers Usama Arif
2026-10-02 9:52 ` [PATCH v8 10/30] mm: make PMD migration-entry splitting explicit Usama Arif
2026-10-02 9:52 ` [PATCH v8 11/30] mm: split PMD swap entries into PTE swap entries Usama Arif
2026-10-02 9:52 ` [PATCH v8 12/30] mm/swap: allow duplicating a range of " Usama Arif
2026-10-02 9:52 ` [PATCH v8 13/30] mm: handle PMD swap entries in fork path Usama Arif
2026-10-02 9:52 ` [PATCH v8 14/30] mm: zswap: reject high-order swap cache allocations backed by zswap Usama Arif
2026-10-02 9:52 ` [PATCH v8 15/30] mm: swap in PMD swap entries as whole THPs during swapoff Usama Arif
2026-10-02 9:52 ` [PATCH v8 16/30] fs/proc: account PMD swap entries in smaps Usama Arif
2026-10-02 9:52 ` [PATCH v8 17/30] mm: handle soft-dirty and uffd-wp on PMD swap entries Usama Arif
2026-10-02 9:52 ` [PATCH v8 18/30] mm/hmm: fault PMD swap entries on demand Usama Arif
2026-10-02 9:52 ` [PATCH v8 19/30] mm: free PMD swap entries in zap_huge_pmd() Usama Arif
2026-10-02 9:52 ` [PATCH v8 20/30] mm/madvise: free PMD swap entries with MADV_FREE Usama Arif
2026-10-02 9:52 ` [PATCH v8 21/30] mm/madvise: skip PMD swap entries for MADV_COLD and MADV_PAGEOUT Usama Arif
2026-10-02 9:52 ` [PATCH v8 22/30] mm/madvise: keep PMD swap entries whole for MADV_GUARD_INSTALL/REMOVE Usama Arif
2026-10-02 9:52 ` [PATCH v8 23/30] mm/mincore: report PMD swap-cache residency Usama Arif
2026-10-02 9:52 ` [PATCH v8 24/30] mm/khugepaged: treat PMD swap entries as mapped THPs Usama Arif
2026-10-02 9:52 ` [PATCH v8 25/30] mm: handle PMD swap entries in MADV_WILLNEED Usama Arif
2026-10-02 9:52 ` [PATCH v8 26/30] mm: handle PMD swap entries in UFFDIO_MOVE Usama Arif
2026-10-02 9:52 ` [PATCH v8 27/30] mm: don't PTE-batch a swap-in over a hardware-poisoned subpage Usama Arif
2026-10-02 9:52 ` [PATCH v8 28/30] mm: handle PMD swap entry faults on swap-in Usama Arif
2026-10-02 9:52 ` [PATCH v8 29/30] mm: install PMD swap entries on swap-out Usama Arif
2026-10-02 9:52 ` [PATCH v8 30/30] selftests/mm: add PMD swap entry tests Usama Arif
2026-10-02 14:28 ` [PATCH v8 00/30] mm: PMD-level swap entries for anonymous THPs David Hildenbrand (Arm)
2026-10-02 15:13 ` Zi Yan [this message]
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