From 10f6646847515b1ab02735c24b04abaf1996f65f Mon Sep 17 00:00:00 2001 From: Thomas Munro Date: Wed, 19 Mar 2025 11:40:56 +1300 Subject: Introduce io_max_combine_limit. The existing io_combine_limit can be changed by users. The new io_max_combine_limit is fixed at server startup time, and functions as a silent clamp on the user setting. That in itself is probably quite useful, but the primary motivation is: aio_init.c allocates shared memory for all asynchronous IOs including some per-block data, and we didn't want to waste memory you'd never used by assuming they could be up to PG_IOV_MAX. This commit already halves the size of 'AioHandleIov' and 'AioHandleData'. A follow-up commit can now expand PG_IOV_MAX without affecting that. Since our GUC system doesn't support dependencies or cross-checks between GUCs, the user-settable one now assigns a "raw" value to io_combine_limit_guc, and the lower of io_combine_limit_guc and io_max_combine_limit is maintained in io_combine_limit. Reviewed-by: Andres Freund (earlier version) Discussion: https://postgr.es/m/CA%2BhUKG%2B2T9p-%2BzM6Eeou-RAJjTML6eit1qn26f9twznX59qtCA%40mail.gmail.com --- src/backend/storage/buffer/bufmgr.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) (limited to 'src/backend/storage/buffer/bufmgr.c') diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index 79ca9d18d07..d04afa5ab9c 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -160,9 +160,12 @@ int maintenance_io_concurrency = DEFAULT_MAINTENANCE_IO_CONCURRENCY; /* * Limit on how many blocks should be handled in single I/O operations. * StartReadBuffers() callers should respect it, as should other operations - * that call smgr APIs directly. + * that call smgr APIs directly. It is computed as the minimum of underlying + * GUCs io_combine_limit_guc and io_max_combine_limit. */ int io_combine_limit = DEFAULT_IO_COMBINE_LIMIT; +int io_combine_limit_guc = DEFAULT_IO_COMBINE_LIMIT; +int io_max_combine_limit = DEFAULT_IO_COMBINE_LIMIT; /* * GUC variables about triggering kernel writeback for buffers written; OS -- cgit v1.2.3