[RFC PATCH 0/2] Use high-order folios in mmap sync RA

[Anatoly Stepanov]

When "fault around" is enabled, 0-order folios might significantly
slowdown filemap_map_pages().

For example when async RA won't be able to start,
we might end up with a large mmap'ed file with 0-orders.

Imagine an access pattern, when we
just access file chunk-by-chunk, where each chunk size equals to RA window,
until every chunk of the file gets loaded into the page cache.

In this case, we never touch RA-marked page, thus async RA wouldn't kick
in, ending with 0-orders covering all the file.

Let's resolve this by starting sync RA with high-order.

(procfs smaps patch is just for showing contpte coverage improvement for arm64)

Based on linux-7.0-rc5

Anatoly Stepanov (2):
  procfs: add contpte info into smaps
  filemap: use high-order folios in filemap sync RA

 fs/proc/task_mmu.c      | 20 +++++++++++++++++---
 include/linux/pagemap.h |  1 +
 mm/filemap.c            |  1 +
 mm/internal.h           |  1 +
 mm/memory.c             |  2 +-
 mm/readahead.c          |  5 +++--
 6 files changed, 24 insertions(+), 6 deletions(-)

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2.34.1