mm: kmemleak: move the struct page scan into a helper

Patch series "mm: kmemleak: batch the struct page scan".

kmemleak walks the struct page array as a scan root and hands it to
scan_block() one page at a time.

scan_block() takes kmemleak_lock with interrupts disabled for the duration
of the call, so the scanner acquires the lock once per online PFN in order
to look at a single 64-byte struct page.

Batching adjacent pages up to that size keeps exactly the same pages under
the same maximum lock hold time, with MAX_SCAN_SIZE / pagesize fewer
acquisitions.

Patch 1 lifts the loop out of __kmemleak_scan() into scan_zone_pages()
with no functional change.  Patch 2 does the batching, which is then
contained in that one function.

This improves the performance due to less atomic operations, which is not
a big deal on a regular machine, but, given kmemleak usually comes with
extra debug options, such as PROVE_LOCKING, DEBUG_SPINLOCK, etc.

For instance, measuring Meta's "debug kernel flavor" on an arm64 hosts,
this improve the scan time by 20%.

It is safe to get more work into scan_block(), given it has the
protections, added by commit eb11f56eeca560 ("mm/kmemleak: stop the task
stack scan early when interrupted")

MAX_SCAN_SIZE is also not a new maximum for a single scan_block() call. 
kmemleak_scan_task_stacks() already hands it a whole task stack in one go.
On arm64 and x86_64 THREAD_SIZE is never below 16 KiB, four times
MAX_SCAN_SIZE, and it is 64 KiB on arm64 with 64K pages.


This patch (of 2):

The struct page scanning loop sits inline in __kmemleak_scan(), nested
three levels deep and sharing the caller's "stop" variable with the
zone walk around it. Move it into scan_zone_pages(), which scans one
zone and returns 1 if scanning should stop.

No functional change; this only makes room for changing how the pages
are handed to scan_block().

Link: https://lore.kernel.org/20260921-b4-kmemleak-page-scan-v1-1-fb97d4801b3a@debian.org
Signed-off-by: Breno Leitao <leitao@debian.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>

0 files changed, 0 insertions, 0 deletions