[v1,0/3] Optimize large folio interaction with deferred split

Message

Ryan Roberts July 17, 2023, 2:31 p.m. UTC

Hi All,

This is a small series in support of my work to enable the use of large folios
for anonymous memory (currently called "FLEXIBLE_THP") [1]. It first makes it
possible to add large, non-pmd-mappable folios to the deferred split queue. Then
it modifies zap_pte_range() to batch-remove spans of physically contiguous pages
from the rmap, which means that in the common case, we elide the need to ever
put the folio on the deferred split queue, thus reducing lock contention and
improving performance.

This becomes more visible once we have lots of large anonymous folios in the
system, and Huang Ying has suggested solving this needs to be a prerequisit for
merging the main FLEXIBLE_THP work.

The series applies on top of v6.5-rc2 and a branch is available at [2].

I don't have a full test run with the latest versions of all the patches on top
of the latest baseline, so not posting results formally. I can get these if
people feel they are neccessary though. But anecdotally, for the kernel
compilation workload, this series reduces kernel time by ~4% and reduces
real-time by ~0.4%, compared with [1].

[1] https://lore.kernel.org/linux-mm/[e-mail]/
[2] https://gitlab.arm.com/linux-arm/linux-rr/-/tree/features/granule_perf/deferredsplit-lkml_v1

Thanks,
Ryan


Ryan Roberts (3):
  mm: Allow deferred splitting of arbitrary large anon folios
  mm: Implement folio_remove_rmap_range()
  mm: Batch-zap large anonymous folio PTE mappings

 include/linux/rmap.h |   2 +
 mm/memory.c          | 119 +++++++++++++++++++++++++++++++++++++++++++
 mm/rmap.c            |  67 +++++++++++++++++++++++-
 3 files changed, 187 insertions(+), 1 deletion(-)

--
2.25.1