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aio: Combine io_uring memory mappings, if supported

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By default io_uring creates a shared memory mapping for each io_uring
instance, leading to a large number of memory mappings. Unfortunately a large
number of memory mappings slows things down, backend exit is particularly
affected.  To address that, newer kernels (6.5) support using user-provided
memory for the memory. By putting the relevant memory into shared memory we
don't need any additional mappings.

On a system with a new enough kernel and liburing, there is no discernible
overhead when doing a pgbench -S -C anymore.

Reported-by: MARK CALLAGHAN <mdcallag@gmail.com>
Reviewed-by: "Burd, Greg" <greg@burd.me>
Reviewed-by: Jim Nasby <jnasby@upgrade.com>
Discussion: https://postgr.es/m/CAFbpF8OA44_UG+RYJcWH9WjF7E3GA6gka3gvH6nsrSnEe9H0NA@mail.gmail.com
Backpatch-through: 18
This commit is contained in:
Andres Freund
2025-07-07 21:03:16 -04:00
parent 55a780e947
commit f54af9f267
6 changed files with 238 additions and 6 deletions
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6
meson.build
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@ -995,6 +995,12 @@ liburingopt = get_option('liburing')
liburing = dependency('liburing', required: liburingopt)
if liburing.found()
cdata.set('USE_LIBURING', 1)
if cc.has_function('io_uring_queue_init_mem',
dependencies: liburing, args: test_c_args)
cdata.set('HAVE_LIBURING_QUEUE_INIT_MEM', 1)
endif
endif