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@xxxxxxx/
[2] https://lore.kernel.org/linux-mm/15a52c3d-9584-449b-8228-1335e0753b04@xxxxxxx/
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
