include/linux/pgtable.h | 59 ++++++++ include/linux/swap.h | 35 +++-- mm/huge_memory.c | 3 - mm/internal.h | 75 +++++++++- mm/madvise.c | 99 +++++++----- mm/memory.c | 17 ++- mm/swap_slots.c | 6 +- mm/swapfile.c | 325 +++++++++++++++++++++++----------------- mm/vmscan.c | 20 +-- 9 files changed, 422 insertions(+), 217 deletions(-)
Hi All,
This series adds support for swapping out multi-size THP (mTHP) without needing
to first split the large folio via split_huge_page_to_list_to_order(). It
closely follows the approach already used to swap-out PMD-sized THP.
There are a couple of reasons for swapping out mTHP without splitting:
- Performance: It is expensive to split a large folio and under extreme memory
pressure some workloads regressed performance when using 64K mTHP vs 4K
small folios because of this extra cost in the swap-out path. This series
not only eliminates the regression but makes it faster to swap out 64K mTHP
vs 4K small folios.
- Memory fragmentation avoidance: If we can avoid splitting a large folio
memory is less likely to become fragmented, making it easier to re-allocate
a large folio in future.
- Performance: Enables a separate series [7] to swap-in whole mTHPs, which
means we won't lose the TLB-efficiency benefits of mTHP once the memory has
been through a swap cycle.
I've done what I thought was the smallest change possible, and as a result, this
approach is only employed when the swap is backed by a non-rotating block device
(just as PMD-sized THP is supported today). Discussion against the RFC concluded
that this is sufficient.
Performance Testing
===================
I've run some swap performance tests on Ampere Altra VM (arm64) with 8 CPUs. The
VM is set up with a 35G block ram device as the swap device and the test is run
from inside a memcg limited to 40G memory. I've then run `usemem` from
vm-scalability with 70 processes, each allocating and writing 1G of memory. I've
repeated everything 6 times and taken the mean performance improvement relative
to 4K page baseline:
| alloc size | baseline | + this series |
| | mm-unstable (~v6.9-rc1) | |
|:-----------|------------------------:|------------------------:|
| 4K Page | 0.0% | 1.3% |
| 64K THP | -13.6% | 46.3% |
| 2M THP | 91.4% | 89.6% |
So with this change, the 64K swap performance goes from a 14% regression to a
46% improvement. While 2M shows a small regression I'm confident that this is
just noise.
---
The series applies against mm-unstable (as of 2024-04-08) after dropping v6 of
this series from it. The performance numbers are from v5. Since the delta is
very small I don't anticipate any performance changes. I'm optimistically hoping
this is the final version.
Changes since v6 [6]
====================
- patch #1
- swap_page_trans_huge_swapped() takes order instead of nr_pages (per Chris)
- patch #2
- Fix bug in swap_pte_batch() to consider swp pte bits (per David)
- Improved docs for clear_not_present_full_ptes() (per David)
- Improved docs for free_swap_and_cache_nr() (per David)
- patch #5
- Split out change to get_swap_pages() interface into own patch (per David)
- patch #6 (was patch #5)
- Improved readability of shrink_folio_list() with longer lines (per David)
Changes since v5 [5]
====================
- patch #2
- Don't bother trying to reclaim swap if none of the entries' refs have gone
to 0 in free_swap_and_cache_nr() (per Huang, Ying)
- patch #5
- Only update THP_SWPOUT_FALLBACK counters for pmd-mappable folios (per
Barry Song)
- patch #6
- Fix bug in madvise_cold_or_pageout_pte_range(): don't continue without ptl
(reported by Barry [8], sysbot [9])
Changes since v4 [4]
====================
- patch #3:
- Added R-B from Huang, Ying - thanks!
- patch #4:
- get_swap_pages() now takes order instead of nr_pages (per Huang, Ying)
- Removed WARN_ON_ONCE() from get_swap_pages()
- Reworded comment for scan_swap_map_try_ssd_cluster() (per Huang, Ying)
- Unified VM_WARN_ON()s in scan_swap_map_slots() to scan: (per Huang, Ying)
- Removed redundant "order == 0" check (per Huang, Ying)
- patch #5:
- Marked list_empty() check with data_race() (per David)
- Added R-B from Barry and David - thanks!
- patch #6:
- Implemented mkold_ptes() generic helper (pre David)
- Enhanced folio_pte_batch() to report any_young (per David)
- madvise_cold_or_pageout_pte_range() sets old in batch (per David)
- Added R-B from Barry - thanks!
Changes since v3 [3]
====================
- Renamed SWAP_NEXT_NULL -> SWAP_NEXT_INVALID (per Huang, Ying)
- Simplified max offset calculation (per Huang, Ying)
- Reinstated struct percpu_cluster to contain per-cluster, per-order `next`
offset (per Huang, Ying)
- Removed swap_alloc_large() and merged its functionality into
scan_swap_map_slots() (per Huang, Ying)
- Avoid extra cost of folio ref and lock due to removal of CLUSTER_FLAG_HUGE
by freeing swap entries in batches (see patch 2) (per DavidH)
- vmscan splits folio if its partially mapped (per Barry Song, DavidH)
- Avoid splitting in MADV_PAGEOUT path (per Barry Song)
- Dropped "mm: swap: Simplify ssd behavior when scanner steals entry" patch
since it's not actually a problem for THP as I first thought.
Changes since v2 [2]
====================
- Reuse scan_swap_map_try_ssd_cluster() between order-0 and order > 0
allocation. This required some refactoring to make everything work nicely
(new patches 2 and 3).
- Fix bug where nr_swap_pages would say there are pages available but the
scanner would not be able to allocate them because they were reserved for the
per-cpu allocator. We now allow stealing of order-0 entries from the high
order per-cpu clusters (in addition to exisiting stealing from order-0
per-cpu clusters).
Changes since v1 [1]
====================
- patch 1:
- Use cluster_set_count() instead of cluster_set_count_flag() in
swap_alloc_cluster() since we no longer have any flag to set. I was unable
to kill cluster_set_count_flag() as proposed against v1 as other call
sites depend explicitly setting flags to 0.
- patch 2:
- Moved large_next[] array into percpu_cluster to make it per-cpu
(recommended by Huang, Ying).
- large_next[] array is dynamically allocated because PMD_ORDER is not
compile-time constant for powerpc (fixes build error).
[1] https://lore.kernel.org/linux-mm/20231010142111.3997780-1-ryan.roberts@arm.com/
[2] https://lore.kernel.org/linux-mm/20231017161302.2518826-1-ryan.roberts@arm.com/
[3] https://lore.kernel.org/linux-mm/20231025144546.577640-1-ryan.roberts@arm.com/
[4] https://lore.kernel.org/linux-mm/20240311150058.1122862-1-ryan.roberts@arm.com/
[5] https://lore.kernel.org/linux-mm/20240327144537.4165578-1-ryan.roberts@arm.com/
[6] https://lore.kernel.org/linux-mm/20240403114032.1162100-1-ryan.roberts@arm.com/
[7] https://lore.kernel.org/linux-mm/20240304081348.197341-1-21cnbao@gmail.com/
[8] https://lore.kernel.org/linux-mm/CAGsJ_4yMOow27WDvN2q=E4HAtDd2PJ=OQ5Pj9DG+6FLWwNuXUw@mail.gmail.com/
[9] https://lore.kernel.org/linux-mm/579d5127-c763-4001-9625-4563a9316ac3@redhat.com/
Thanks,
Ryan
Ryan Roberts (7):
mm: swap: Remove CLUSTER_FLAG_HUGE from swap_cluster_info:flags
mm: swap: free_swap_and_cache_nr() as batched free_swap_and_cache()
mm: swap: Simplify struct percpu_cluster
mm: swap: Update get_swap_pages() to take folio order
mm: swap: Allow storage of all mTHP orders
mm: vmscan: Avoid split during shrink_folio_list()
mm: madvise: Avoid split during MADV_PAGEOUT and MADV_COLD
include/linux/pgtable.h | 59 ++++++++
include/linux/swap.h | 35 +++--
mm/huge_memory.c | 3 -
mm/internal.h | 75 +++++++++-
mm/madvise.c | 99 +++++++-----
mm/memory.c | 17 ++-
mm/swap_slots.c | 6 +-
mm/swapfile.c | 325 +++++++++++++++++++++++-----------------
mm/vmscan.c | 20 +--
9 files changed, 422 insertions(+), 217 deletions(-)
--
2.25.1
On Mon, Apr 8, 2024 at 11:40 AM Ryan Roberts <ryan.roberts@arm.com> wrote:
>
> Hi All,
>
> This series adds support for swapping out multi-size THP (mTHP) without needing
> to first split the large folio via split_huge_page_to_list_to_order(). It
> closely follows the approach already used to swap-out PMD-sized THP.
>
> There are a couple of reasons for swapping out mTHP without splitting:
>
> - Performance: It is expensive to split a large folio and under extreme memory
> pressure some workloads regressed performance when using 64K mTHP vs 4K
> small folios because of this extra cost in the swap-out path. This series
> not only eliminates the regression but makes it faster to swap out 64K mTHP
> vs 4K small folios.
>
> - Memory fragmentation avoidance: If we can avoid splitting a large folio
> memory is less likely to become fragmented, making it easier to re-allocate
> a large folio in future.
>
> - Performance: Enables a separate series [7] to swap-in whole mTHPs, which
> means we won't lose the TLB-efficiency benefits of mTHP once the memory has
> been through a swap cycle.
>
> I've done what I thought was the smallest change possible, and as a result, this
> approach is only employed when the swap is backed by a non-rotating block device
> (just as PMD-sized THP is supported today). Discussion against the RFC concluded
> that this is sufficient.
>
>
> Performance Testing
> ===================
>
> I've run some swap performance tests on Ampere Altra VM (arm64) with 8 CPUs. The
> VM is set up with a 35G block ram device as the swap device and the test is run
> from inside a memcg limited to 40G memory. I've then run `usemem` from
> vm-scalability with 70 processes, each allocating and writing 1G of memory. I've
> repeated everything 6 times and taken the mean performance improvement relative
> to 4K page baseline:
>
> | alloc size | baseline | + this series |
> | | mm-unstable (~v6.9-rc1) | |
> |:-----------|------------------------:|------------------------:|
> | 4K Page | 0.0% | 1.3% |
> | 64K THP | -13.6% | 46.3% |
> | 2M THP | 91.4% | 89.6% |
>
> So with this change, the 64K swap performance goes from a 14% regression to a
> 46% improvement. While 2M shows a small regression I'm confident that this is
> just noise.
>
> ---
> The series applies against mm-unstable (as of 2024-04-08) after dropping v6 of
> this series from it. The performance numbers are from v5. Since the delta is
> very small I don't anticipate any performance changes. I'm optimistically hoping
> this is the final version.
>
>
> Changes since v6 [6]
> ====================
>
> - patch #1
> - swap_page_trans_huge_swapped() takes order instead of nr_pages (per Chris)
> - patch #2
> - Fix bug in swap_pte_batch() to consider swp pte bits (per David)
> - Improved docs for clear_not_present_full_ptes() (per David)
> - Improved docs for free_swap_and_cache_nr() (per David)
> - patch #5
> - Split out change to get_swap_pages() interface into own patch (per David)
> - patch #6 (was patch #5)
> - Improved readability of shrink_folio_list() with longer lines (per David)
>
>
> Changes since v5 [5]
> ====================
>
> - patch #2
> - Don't bother trying to reclaim swap if none of the entries' refs have gone
> to 0 in free_swap_and_cache_nr() (per Huang, Ying)
> - patch #5
> - Only update THP_SWPOUT_FALLBACK counters for pmd-mappable folios (per
> Barry Song)
> - patch #6
> - Fix bug in madvise_cold_or_pageout_pte_range(): don't continue without ptl
> (reported by Barry [8], sysbot [9])
>
>
> Changes since v4 [4]
> ====================
>
> - patch #3:
> - Added R-B from Huang, Ying - thanks!
> - patch #4:
> - get_swap_pages() now takes order instead of nr_pages (per Huang, Ying)
> - Removed WARN_ON_ONCE() from get_swap_pages()
> - Reworded comment for scan_swap_map_try_ssd_cluster() (per Huang, Ying)
> - Unified VM_WARN_ON()s in scan_swap_map_slots() to scan: (per Huang, Ying)
> - Removed redundant "order == 0" check (per Huang, Ying)
> - patch #5:
> - Marked list_empty() check with data_race() (per David)
> - Added R-B from Barry and David - thanks!
> - patch #6:
> - Implemented mkold_ptes() generic helper (pre David)
> - Enhanced folio_pte_batch() to report any_young (per David)
> - madvise_cold_or_pageout_pte_range() sets old in batch (per David)
> - Added R-B from Barry - thanks!
>
>
> Changes since v3 [3]
> ====================
>
> - Renamed SWAP_NEXT_NULL -> SWAP_NEXT_INVALID (per Huang, Ying)
> - Simplified max offset calculation (per Huang, Ying)
> - Reinstated struct percpu_cluster to contain per-cluster, per-order `next`
> offset (per Huang, Ying)
> - Removed swap_alloc_large() and merged its functionality into
> scan_swap_map_slots() (per Huang, Ying)
> - Avoid extra cost of folio ref and lock due to removal of CLUSTER_FLAG_HUGE
> by freeing swap entries in batches (see patch 2) (per DavidH)
> - vmscan splits folio if its partially mapped (per Barry Song, DavidH)
> - Avoid splitting in MADV_PAGEOUT path (per Barry Song)
> - Dropped "mm: swap: Simplify ssd behavior when scanner steals entry" patch
> since it's not actually a problem for THP as I first thought.
>
>
> Changes since v2 [2]
> ====================
>
> - Reuse scan_swap_map_try_ssd_cluster() between order-0 and order > 0
> allocation. This required some refactoring to make everything work nicely
> (new patches 2 and 3).
> - Fix bug where nr_swap_pages would say there are pages available but the
> scanner would not be able to allocate them because they were reserved for the
> per-cpu allocator. We now allow stealing of order-0 entries from the high
> order per-cpu clusters (in addition to exisiting stealing from order-0
> per-cpu clusters).
>
>
> Changes since v1 [1]
> ====================
>
> - patch 1:
> - Use cluster_set_count() instead of cluster_set_count_flag() in
> swap_alloc_cluster() since we no longer have any flag to set. I was unable
> to kill cluster_set_count_flag() as proposed against v1 as other call
> sites depend explicitly setting flags to 0.
> - patch 2:
> - Moved large_next[] array into percpu_cluster to make it per-cpu
> (recommended by Huang, Ying).
> - large_next[] array is dynamically allocated because PMD_ORDER is not
> compile-time constant for powerpc (fixes build error).
>
>
> [1] https://lore.kernel.org/linux-mm/20231010142111.3997780-1-ryan.roberts@arm.com/
> [2] https://lore.kernel.org/linux-mm/20231017161302.2518826-1-ryan.roberts@arm.com/
> [3] https://lore.kernel.org/linux-mm/20231025144546.577640-1-ryan.roberts@arm.com/
> [4] https://lore.kernel.org/linux-mm/20240311150058.1122862-1-ryan.roberts@arm.com/
> [5] https://lore.kernel.org/linux-mm/20240327144537.4165578-1-ryan.roberts@arm.com/
> [6] https://lore.kernel.org/linux-mm/20240403114032.1162100-1-ryan.roberts@arm.com/
> [7] https://lore.kernel.org/linux-mm/20240304081348.197341-1-21cnbao@gmail.com/
> [8] https://lore.kernel.org/linux-mm/CAGsJ_4yMOow27WDvN2q=E4HAtDd2PJ=OQ5Pj9DG+6FLWwNuXUw@mail.gmail.com/
> [9] https://lore.kernel.org/linux-mm/579d5127-c763-4001-9625-4563a9316ac3@redhat.com/
>
> Thanks,
> Ryan
>
> Ryan Roberts (7):
> mm: swap: Remove CLUSTER_FLAG_HUGE from swap_cluster_info:flags
> mm: swap: free_swap_and_cache_nr() as batched free_swap_and_cache()
> mm: swap: Simplify struct percpu_cluster
> mm: swap: Update get_swap_pages() to take folio order
> mm: swap: Allow storage of all mTHP orders
> mm: vmscan: Avoid split during shrink_folio_list()
> mm: madvise: Avoid split during MADV_PAGEOUT and MADV_COLD
+Zi Yan
While looking at the page splitting code, I noticed that
split_huge_page_to_list_to_order() will refuse to split a folio in the
swapcache to any order higher than 0. It has the following check:
if (new_order) {
/* Only swapping a whole PMD-mapped folio is supported */
if (folio_test_swapcache(folio))
return -EINVAL;
...
}
I am guessing with this series this may no longer be applicable?
>
> include/linux/pgtable.h | 59 ++++++++
> include/linux/swap.h | 35 +++--
> mm/huge_memory.c | 3 -
> mm/internal.h | 75 +++++++++-
> mm/madvise.c | 99 +++++++-----
> mm/memory.c | 17 ++-
> mm/swap_slots.c | 6 +-
> mm/swapfile.c | 325 +++++++++++++++++++++++-----------------
> mm/vmscan.c | 20 +--
> 9 files changed, 422 insertions(+), 217 deletions(-)
>
> --
> 2.25.1
>
>
On 3 Jun 2024, at 14:18, Yosry Ahmed wrote:
> On Mon, Apr 8, 2024 at 11:40 AM Ryan Roberts <ryan.roberts@arm.com> wrote:
>>
>> Hi All,
>>
>> This series adds support for swapping out multi-size THP (mTHP) without needing
>> to first split the large folio via split_huge_page_to_list_to_order(). It
>> closely follows the approach already used to swap-out PMD-sized THP.
>>
>> There are a couple of reasons for swapping out mTHP without splitting:
>>
>> - Performance: It is expensive to split a large folio and under extreme memory
>> pressure some workloads regressed performance when using 64K mTHP vs 4K
>> small folios because of this extra cost in the swap-out path. This series
>> not only eliminates the regression but makes it faster to swap out 64K mTHP
>> vs 4K small folios.
>>
>> - Memory fragmentation avoidance: If we can avoid splitting a large folio
>> memory is less likely to become fragmented, making it easier to re-allocate
>> a large folio in future.
>>
>> - Performance: Enables a separate series [7] to swap-in whole mTHPs, which
>> means we won't lose the TLB-efficiency benefits of mTHP once the memory has
>> been through a swap cycle.
>>
>> I've done what I thought was the smallest change possible, and as a result, this
>> approach is only employed when the swap is backed by a non-rotating block device
>> (just as PMD-sized THP is supported today). Discussion against the RFC concluded
>> that this is sufficient.
>>
>>
>> Performance Testing
>> ===================
>>
>> I've run some swap performance tests on Ampere Altra VM (arm64) with 8 CPUs. The
>> VM is set up with a 35G block ram device as the swap device and the test is run
>> from inside a memcg limited to 40G memory. I've then run `usemem` from
>> vm-scalability with 70 processes, each allocating and writing 1G of memory. I've
>> repeated everything 6 times and taken the mean performance improvement relative
>> to 4K page baseline:
>>
>> | alloc size | baseline | + this series |
>> | | mm-unstable (~v6.9-rc1) | |
>> |:-----------|------------------------:|------------------------:|
>> | 4K Page | 0.0% | 1.3% |
>> | 64K THP | -13.6% | 46.3% |
>> | 2M THP | 91.4% | 89.6% |
>>
>> So with this change, the 64K swap performance goes from a 14% regression to a
>> 46% improvement. While 2M shows a small regression I'm confident that this is
>> just noise.
>>
>> ---
>> The series applies against mm-unstable (as of 2024-04-08) after dropping v6 of
>> this series from it. The performance numbers are from v5. Since the delta is
>> very small I don't anticipate any performance changes. I'm optimistically hoping
>> this is the final version.
>>
>>
>> Changes since v6 [6]
>> ====================
>>
>> - patch #1
>> - swap_page_trans_huge_swapped() takes order instead of nr_pages (per Chris)
>> - patch #2
>> - Fix bug in swap_pte_batch() to consider swp pte bits (per David)
>> - Improved docs for clear_not_present_full_ptes() (per David)
>> - Improved docs for free_swap_and_cache_nr() (per David)
>> - patch #5
>> - Split out change to get_swap_pages() interface into own patch (per David)
>> - patch #6 (was patch #5)
>> - Improved readability of shrink_folio_list() with longer lines (per David)
>>
>>
>> Changes since v5 [5]
>> ====================
>>
>> - patch #2
>> - Don't bother trying to reclaim swap if none of the entries' refs have gone
>> to 0 in free_swap_and_cache_nr() (per Huang, Ying)
>> - patch #5
>> - Only update THP_SWPOUT_FALLBACK counters for pmd-mappable folios (per
>> Barry Song)
>> - patch #6
>> - Fix bug in madvise_cold_or_pageout_pte_range(): don't continue without ptl
>> (reported by Barry [8], sysbot [9])
>>
>>
>> Changes since v4 [4]
>> ====================
>>
>> - patch #3:
>> - Added R-B from Huang, Ying - thanks!
>> - patch #4:
>> - get_swap_pages() now takes order instead of nr_pages (per Huang, Ying)
>> - Removed WARN_ON_ONCE() from get_swap_pages()
>> - Reworded comment for scan_swap_map_try_ssd_cluster() (per Huang, Ying)
>> - Unified VM_WARN_ON()s in scan_swap_map_slots() to scan: (per Huang, Ying)
>> - Removed redundant "order == 0" check (per Huang, Ying)
>> - patch #5:
>> - Marked list_empty() check with data_race() (per David)
>> - Added R-B from Barry and David - thanks!
>> - patch #6:
>> - Implemented mkold_ptes() generic helper (pre David)
>> - Enhanced folio_pte_batch() to report any_young (per David)
>> - madvise_cold_or_pageout_pte_range() sets old in batch (per David)
>> - Added R-B from Barry - thanks!
>>
>>
>> Changes since v3 [3]
>> ====================
>>
>> - Renamed SWAP_NEXT_NULL -> SWAP_NEXT_INVALID (per Huang, Ying)
>> - Simplified max offset calculation (per Huang, Ying)
>> - Reinstated struct percpu_cluster to contain per-cluster, per-order `next`
>> offset (per Huang, Ying)
>> - Removed swap_alloc_large() and merged its functionality into
>> scan_swap_map_slots() (per Huang, Ying)
>> - Avoid extra cost of folio ref and lock due to removal of CLUSTER_FLAG_HUGE
>> by freeing swap entries in batches (see patch 2) (per DavidH)
>> - vmscan splits folio if its partially mapped (per Barry Song, DavidH)
>> - Avoid splitting in MADV_PAGEOUT path (per Barry Song)
>> - Dropped "mm: swap: Simplify ssd behavior when scanner steals entry" patch
>> since it's not actually a problem for THP as I first thought.
>>
>>
>> Changes since v2 [2]
>> ====================
>>
>> - Reuse scan_swap_map_try_ssd_cluster() between order-0 and order > 0
>> allocation. This required some refactoring to make everything work nicely
>> (new patches 2 and 3).
>> - Fix bug where nr_swap_pages would say there are pages available but the
>> scanner would not be able to allocate them because they were reserved for the
>> per-cpu allocator. We now allow stealing of order-0 entries from the high
>> order per-cpu clusters (in addition to exisiting stealing from order-0
>> per-cpu clusters).
>>
>>
>> Changes since v1 [1]
>> ====================
>>
>> - patch 1:
>> - Use cluster_set_count() instead of cluster_set_count_flag() in
>> swap_alloc_cluster() since we no longer have any flag to set. I was unable
>> to kill cluster_set_count_flag() as proposed against v1 as other call
>> sites depend explicitly setting flags to 0.
>> - patch 2:
>> - Moved large_next[] array into percpu_cluster to make it per-cpu
>> (recommended by Huang, Ying).
>> - large_next[] array is dynamically allocated because PMD_ORDER is not
>> compile-time constant for powerpc (fixes build error).
>>
>>
>> [1] https://lore.kernel.org/linux-mm/20231010142111.3997780-1-ryan.roberts@arm.com/
>> [2] https://lore.kernel.org/linux-mm/20231017161302.2518826-1-ryan.roberts@arm.com/
>> [3] https://lore.kernel.org/linux-mm/20231025144546.577640-1-ryan.roberts@arm.com/
>> [4] https://lore.kernel.org/linux-mm/20240311150058.1122862-1-ryan.roberts@arm.com/
>> [5] https://lore.kernel.org/linux-mm/20240327144537.4165578-1-ryan.roberts@arm.com/
>> [6] https://lore.kernel.org/linux-mm/20240403114032.1162100-1-ryan.roberts@arm.com/
>> [7] https://lore.kernel.org/linux-mm/20240304081348.197341-1-21cnbao@gmail.com/
>> [8] https://lore.kernel.org/linux-mm/CAGsJ_4yMOow27WDvN2q=E4HAtDd2PJ=OQ5Pj9DG+6FLWwNuXUw@mail.gmail.com/
>> [9] https://lore.kernel.org/linux-mm/579d5127-c763-4001-9625-4563a9316ac3@redhat.com/
>>
>> Thanks,
>> Ryan
>>
>> Ryan Roberts (7):
>> mm: swap: Remove CLUSTER_FLAG_HUGE from swap_cluster_info:flags
>> mm: swap: free_swap_and_cache_nr() as batched free_swap_and_cache()
>> mm: swap: Simplify struct percpu_cluster
>> mm: swap: Update get_swap_pages() to take folio order
>> mm: swap: Allow storage of all mTHP orders
>> mm: vmscan: Avoid split during shrink_folio_list()
>> mm: madvise: Avoid split during MADV_PAGEOUT and MADV_COLD
>
> +Zi Yan
>
> While looking at the page splitting code, I noticed that
> split_huge_page_to_list_to_order() will refuse to split a folio in the
> swapcache to any order higher than 0. It has the following check:
>
> if (new_order) {
> /* Only swapping a whole PMD-mapped folio is supported */
> if (folio_test_swapcache(folio))
> return -EINVAL;
> ...
> }
>
> I am guessing with this series this may no longer be applicable?
Yes, you can remove it but please make sure the swapcache code below is right[1].
[1] https://elixir.bootlin.com/linux/v6.10-rc2/source/mm/huge_memory.c#L2868
Best Regards,
Yan, Zi
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