From b7a4bd996a0a296eeda9a3938ff965131825cb9f Mon Sep 17 00:00:00 2001 From: Thomas Munro Date: Wed, 12 Feb 2025 13:52:22 +1300 Subject: [PATCH v3 2/3] Introduce max_io_combine_limit. The existing io_combine_limit parameter can be set by users. The new max_io_combine_limit parameter can be set only at server startup time, and applies as a silent limit on top of that. Since our GUC system doesn't allow dependencies between GUCs, the user-settable one assigns a "raw" value to io_combine_limit_guc, and the minimum of io_combine_limit_guc and max_io_combine_limit is maintained in io_combine_limit. In other words, code should continue to refer to io_combine_limit directly, and io_combine_limit_guc is an implementation detail that could eventually be removed if the GUC system ever learns how to deal with dependencies. max_io_combine_limit allows the administrator to cap the total I/O size system-wide, and also provides a way for proposed AIO patches to know what the maximum could possibly be when allocating related memory at server startup, without having to assume it is the compile-time maximum MAX_IO_COMBINE_LIMIT. This paves the way for increasing the latter. Reviewed-by: Andres Freund Discussion: https://postgr.es/m/CA%2BhUKG%2B2T9p-%2BzM6Eeou-RAJjTML6eit1qn26f9twznX59qtCA%40mail.gmail.com --- doc/src/sgml/config.sgml | 23 ++++++++++++++++++- src/backend/commands/variable.c | 18 +++++++++++++++ src/backend/storage/buffer/bufmgr.c | 5 +++- src/backend/utils/misc/guc_tables.c | 16 ++++++++++++- src/backend/utils/misc/postgresql.conf.sample | 2 ++ src/include/storage/bufmgr.h | 4 +++- src/include/utils/guc_hooks.h | 2 ++ 7 files changed, 66 insertions(+), 4 deletions(-) diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml index e55700f35b8..68ba7cc7980 100644 --- a/doc/src/sgml/config.sgml +++ b/doc/src/sgml/config.sgml @@ -2631,6 +2631,24 @@ include_dir 'conf.d' + + max_io_combine_limit (integer) + + max_io_combine_limit configuration parameter + + + + + Controls the largest I/O size in operations that combine I/O, and silently + limits the user-settable parameter io_combine_limit. + This parameter can only be set in + the postgresql.conf file or on the server + command line. + The default is 128kB. + + + + io_combine_limit (integer) @@ -2639,7 +2657,10 @@ include_dir 'conf.d' - Controls the largest I/O size in operations that combine I/O. + Controls the largest I/O size in operations that combine I/O. If set + higher than the max_io_combine_limit parameter, the + smaller value will silently be used instead, so both may need to be raised + to increase the I/O size. The default is 128kB. diff --git a/src/backend/commands/variable.c b/src/backend/commands/variable.c index 4ad6e236d69..fab8f2c7958 100644 --- a/src/backend/commands/variable.c +++ b/src/backend/commands/variable.c @@ -1156,6 +1156,24 @@ assign_maintenance_io_concurrency(int newval, void *extra) #endif } +/* + * GUC assign hooks that recompute io_combine_limit whenever + * io_combine_limit_guc and max_io_combine_limit are changed. These are needed + * because the GUC subsystem doesn't support dependencies between GUCs, and + * they may be assigned in either order. + */ +void +assign_max_io_combine_limit(int newval, void *extra) +{ + max_io_combine_limit = newval; + io_combine_limit = Min(max_io_combine_limit, io_combine_limit_guc); +} +void +assign_io_combine_limit(int newval, void *extra) +{ + io_combine_limit_guc = newval; + io_combine_limit = Min(max_io_combine_limit, io_combine_limit_guc); +} /* * These show hooks just exist because we want to show the values in octal. diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index 7915ed624c1..af97d08b0ae 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 max_io_combine_limit. */ int io_combine_limit = DEFAULT_IO_COMBINE_LIMIT; +int io_combine_limit_guc = DEFAULT_IO_COMBINE_LIMIT; +int max_io_combine_limit = DEFAULT_IO_COMBINE_LIMIT; /* * GUC variables about triggering kernel writeback for buffers written; OS diff --git a/src/backend/utils/misc/guc_tables.c b/src/backend/utils/misc/guc_tables.c index ad25cbb39c5..d1cb93562d1 100644 --- a/src/backend/utils/misc/guc_tables.c +++ b/src/backend/utils/misc/guc_tables.c @@ -3240,6 +3240,20 @@ struct config_int ConfigureNamesInt[] = NULL }, + { + {"max_io_combine_limit", + PGC_POSTMASTER, + RESOURCES_IO, + gettext_noop("System-wide limit applied to io_combine_limit."), + NULL, + GUC_UNIT_BLOCKS + }, + &max_io_combine_limit, + DEFAULT_IO_COMBINE_LIMIT, + 1, MAX_IO_COMBINE_LIMIT, + NULL, assign_max_io_combine_limit, NULL + }, + { {"io_combine_limit", PGC_USERSET, @@ -3251,7 +3265,7 @@ struct config_int ConfigureNamesInt[] = &io_combine_limit, DEFAULT_IO_COMBINE_LIMIT, 1, MAX_IO_COMBINE_LIMIT, - NULL, NULL, NULL + NULL, assign_io_combine_limit, NULL }, { diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample index 5362ff80519..1d63f9e5f36 100644 --- a/src/backend/utils/misc/postgresql.conf.sample +++ b/src/backend/utils/misc/postgresql.conf.sample @@ -200,6 +200,8 @@ #backend_flush_after = 0 # measured in pages, 0 disables #effective_io_concurrency = 1 # 1-1000; 0 disables prefetching #maintenance_io_concurrency = 10 # 1-1000; 0 disables prefetching +#max_io_combine_limit = 128kB # usually 1-32 blocks (depends on OS) + # (change requires restart) #io_combine_limit = 128kB # usually 1-32 blocks (depends on OS) # - Worker Processes - diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 7c1e4316dde..91a2f548c3a 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -163,7 +163,9 @@ extern PGDLLIMPORT int maintenance_io_concurrency; #define MAX_IO_COMBINE_LIMIT PG_IOV_MAX #define DEFAULT_IO_COMBINE_LIMIT Min(MAX_IO_COMBINE_LIMIT, (128 * 1024) / BLCKSZ) -extern PGDLLIMPORT int io_combine_limit; +extern PGDLLIMPORT int io_combine_limit; /* min of the two GUCs below */ +extern PGDLLIMPORT int io_combine_limit_guc; +extern PGDLLIMPORT int max_io_combine_limit; extern PGDLLIMPORT int checkpoint_flush_after; extern PGDLLIMPORT int backend_flush_after; diff --git a/src/include/utils/guc_hooks.h b/src/include/utils/guc_hooks.h index 951451a9765..8f52af2fcee 100644 --- a/src/include/utils/guc_hooks.h +++ b/src/include/utils/guc_hooks.h @@ -82,6 +82,8 @@ extern const char *show_log_timezone(void); extern bool check_maintenance_io_concurrency(int *newval, void **extra, GucSource source); extern void assign_maintenance_io_concurrency(int newval, void *extra); +extern void assign_max_io_combine_limit(int newval, void *extra); +extern void assign_io_combine_limit(int newval, void *extra); extern bool check_max_slot_wal_keep_size(int *newval, void **extra, GucSource source); extern void assign_max_wal_size(int newval, void *extra); -- 2.48.1