Add a flag that allows to disable merging per slab. This can be used for more fine grained control over the caches or for debugging builds where separate slabs can verify that no objects leak. The slab_nomerge boot option is too coarse and would need to be enabled on all testing hosts. There are some other ways how to disable merging, e.g. a slab constructor but this disables poisoning besides that it adds additional overhead. Other flags are internal and may have other semantics. A concrete example what motivates the flag. During 'btrfs balance' slab top reported huge increase in caches like 1330095 1330095 100% 0.10K 34105 39 136420K Acpi-ParseExt 1734684 1734684 100% 0.14K 61953 28 247812K pid_namespace 8244036 6873075 83% 0.11K 229001 36 916004K khugepaged_mm_slot which was confusing and that it's because of slab merging was not the first idea. After rebooting with slab_nomerge all the caches were from btrfs_ namespace as expected. Signed-off-by: David Sterba <dsterba@xxxxxxxx> --- include/linux/slab.h | 3 +++ mm/slab_common.c | 2 +- 2 files changed, 4 insertions(+), 1 deletion(-) diff --git a/include/linux/slab.h b/include/linux/slab.h index 6b3e155b70bf..06b94dfbce65 100644 --- a/include/linux/slab.h +++ b/include/linux/slab.h @@ -106,6 +106,9 @@ /* Avoid kmemleak tracing */ #define SLAB_NOLEAKTRACE ((slab_flags_t __force)0x00800000U) +/* Don't merge slab */ +#define SLAB_NO_MERGE ((slab_flags_t __force)0x01000000U) + /* Fault injection mark */ #ifdef CONFIG_FAILSLAB # define SLAB_FAILSLAB ((slab_flags_t __force)0x02000000U) diff --git a/mm/slab_common.c b/mm/slab_common.c index 607249785c07..0e0a617eae7d 100644 --- a/mm/slab_common.c +++ b/mm/slab_common.c @@ -47,7 +47,7 @@ static DECLARE_WORK(slab_caches_to_rcu_destroy_work, */ #define SLAB_NEVER_MERGE (SLAB_RED_ZONE | SLAB_POISON | SLAB_STORE_USER | \ SLAB_TRACE | SLAB_TYPESAFE_BY_RCU | SLAB_NOLEAKTRACE | \ - SLAB_FAILSLAB | kasan_never_merge()) + SLAB_FAILSLAB | SLAB_NO_MERGE | kasan_never_merge()) #define SLAB_MERGE_SAME (SLAB_RECLAIM_ACCOUNT | SLAB_CACHE_DMA | \ SLAB_CACHE_DMA32 | SLAB_ACCOUNT) -- 2.40.0
