Messages in this thread | | | From | Ryan Roberts <> | Subject | [PATCH v2 0/2] Swap-out small-sized THP without splitting | Date | Tue, 17 Oct 2023 17:13:00 +0100 |
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Hi All,
This is v2 of a series to add support for swapping out small-sized THP without needing to first split the large folio via __split_huge_page(). It closely follows the approach already used by PMD-sized THP.
"Small-sized THP" is an upcoming feature that enables performance improvements by allocating large folios for anonymous memory, where the large folio size is smaller than the traditional PMD-size. See [2].
In some circumstances I've observed a performance regression (see patch 2 for details), and this series is an attempt to fix the regression in advance of merging small-sized THP support.
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 probably sufficient.
The series applies against mm-unstable (3fb06e6d0a6f)
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).
Thanks, Ryan
[1] https://lore.kernel.org/linux-mm/20231010142111.3997780-1-ryan.roberts@arm.com/ [2] https://lore.kernel.org/linux-mm/15a52c3d-9584-449b-8228-1335e0753b04@arm.com/
Ryan Roberts (2): mm: swap: Remove CLUSTER_FLAG_HUGE from swap_cluster_info:flags mm: swap: Swap-out small-sized THP without splitting
include/linux/swap.h | 16 +++--- mm/huge_memory.c | 3 -- mm/swapfile.c | 119 ++++++++++++++++++++++++------------------- mm/vmscan.c | 10 ++-- 4 files changed, 78 insertions(+), 70 deletions(-)
-- 2.25.1
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