diff mbox series

[07/12] mm, slab: ignore SLAB_RECLAIM_ACCOUNT with CONFIG_SLUB_TINY

Message ID 20221121171202.22080-8-vbabka@suse.cz
State New
Headers
Series Introduce CONFIG_SLUB_TINY and deprecate SLOB |

Commit Message

Vlastimil Babka Nov. 21, 2022, 5:11 p.m. UTC 
  SLAB_RECLAIM_ACCOUNT caches allocate their slab pages with
__GFP_RECLAIMABLE and can help against fragmentation by grouping pages
by mobility, but on tiny systems mobility grouping is likely disabled
anyway and ignoring SLAB_RECLAIM_ACCOUNT might instead lead to merging
of caches that are made incompatible just by the flag.

Thus with CONFIG_SLUB_TINY, make SLAB_RECLAIM_ACCOUNT ineffective.

Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
---
 include/linux/slab.h | 4 ++++
 1 file changed, 4 insertions(+)

Comments

Roman Gushchin Nov. 24, 2022, 1:20 a.m. UTC | #1 
On Mon, Nov 21, 2022 at 06:11:57PM +0100, Vlastimil Babka wrote:
> SLAB_RECLAIM_ACCOUNT caches allocate their slab pages with
> __GFP_RECLAIMABLE and can help against fragmentation by grouping pages
> by mobility, but on tiny systems mobility grouping is likely disabled
> anyway and ignoring SLAB_RECLAIM_ACCOUNT might instead lead to merging
> of caches that are made incompatible just by the flag.
> 
> Thus with CONFIG_SLUB_TINY, make SLAB_RECLAIM_ACCOUNT ineffective.

Hm, do you see disabling all kernel memory accounting functionality
with COFNIG_SLUB_TINY? I'd say yes. But in this case need to be consistent
and disable it alltogether.

Thanks!
Vlastimil Babka Nov. 24, 2022, 9:09 a.m. UTC | #2 
On 11/24/22 02:20, Roman Gushchin wrote:
> On Mon, Nov 21, 2022 at 06:11:57PM +0100, Vlastimil Babka wrote:
>> SLAB_RECLAIM_ACCOUNT caches allocate their slab pages with
>> __GFP_RECLAIMABLE and can help against fragmentation by grouping pages
>> by mobility, but on tiny systems mobility grouping is likely disabled
>> anyway and ignoring SLAB_RECLAIM_ACCOUNT might instead lead to merging
>> of caches that are made incompatible just by the flag.
>> 
>> Thus with CONFIG_SLUB_TINY, make SLAB_RECLAIM_ACCOUNT ineffective.
> 
> Hm, do you see disabling all kernel memory accounting functionality
> with COFNIG_SLUB_TINY? I'd say yes. But in this case need to be consistent
> and disable it alltogether.

SLAB_RECLAIM_ACCOUNT is kinda misnomer these days, as the only thing it does
is to add __GFP_RECLAIMABLE to cache's gfp flags for the page allocator's
mobility grouping. I guess the "ACCOUNT" part comes from being counted
towards SReclaimable (vs SUnreclaim) in /proc/meminfo.

So currently SLUB_TINY has no effect on MEMCG_KMEM (which you probably
meant). Using those two together has little sense and had I stumbled while
making this series upon a code that would become complicated, I would have
made SLUB_TINY disable MEMCG_KMEM, but that didn't happen so I left as is
for now.

> Thanks!
Christoph Lameter Nov. 24, 2022, 9:21 a.m. UTC | #3 
On Thu, 24 Nov 2022, Vlastimil Babka wrote:

> SLAB_RECLAIM_ACCOUNT is kinda misnomer these days, as the only thing it does
> is to add __GFP_RECLAIMABLE to cache's gfp flags for the page allocator's
> mobility grouping. I guess the "ACCOUNT" part comes from being counted
> towards SReclaimable (vs SUnreclaim) in /proc/meminfo.

Well these Sreclaimable etc counters visible in /proc/meminfo are used in
the reclaim logic and are quite important there.
Vlastimil Babka Nov. 27, 2022, 11:11 p.m. UTC | #4 
On 11/21/22 18:11, Vlastimil Babka wrote:
> SLAB_RECLAIM_ACCOUNT caches allocate their slab pages with
> __GFP_RECLAIMABLE and can help against fragmentation by grouping pages
> by mobility, but on tiny systems mobility grouping is likely disabled
> anyway and ignoring SLAB_RECLAIM_ACCOUNT might instead lead to merging
> of caches that are made incompatible just by the flag.
> 
> Thus with CONFIG_SLUB_TINY, make SLAB_RECLAIM_ACCOUNT ineffective.
> 
> Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
> ---
>  include/linux/slab.h | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/include/linux/slab.h b/include/linux/slab.h
> index 3ce9474c90ab..1cbbda03ad06 100644
> --- a/include/linux/slab.h
> +++ b/include/linux/slab.h
> @@ -129,7 +129,11 @@
>  
>  /* The following flags affect the page allocator grouping pages by mobility */
>  /* Objects are reclaimable */
> +#ifndef CONFIG_SLUB_TINY
>  #define SLAB_RECLAIM_ACCOUNT	((slab_flags_t __force)0x00020000U)
> +#else
> +#define SLAB_RECLAIM_ACCOUNT	0

Updating the last line above to:
#define SLAB_RECLAIM_ACCOUNT      ((slab_flags_t __force)0)

In response to:
https://lore.kernel.org/all/202211280441.yCEecX9z-lkp@intel.com/

Yeah it probably means that the other pre-existing flag variants that
#define to 0 should be also adjusted to avoid these issues, but not as part
of this series.

> +#endif
>  #define SLAB_TEMPORARY		SLAB_RECLAIM_ACCOUNT	/* Objects are short-lived */
>  
>  /*
diff mbox series

Patch

diff --git a/include/linux/slab.h b/include/linux/slab.h
index 3ce9474c90ab..1cbbda03ad06 100644
--- a/include/linux/slab.h
+++ b/include/linux/slab.h
@@ -129,7 +129,11 @@ 
 
 /* The following flags affect the page allocator grouping pages by mobility */
 /* Objects are reclaimable */
+#ifndef CONFIG_SLUB_TINY
 #define SLAB_RECLAIM_ACCOUNT	((slab_flags_t __force)0x00020000U)
+#else
+#define SLAB_RECLAIM_ACCOUNT	0
+#endif
 #define SLAB_TEMPORARY		SLAB_RECLAIM_ACCOUNT	/* Objects are short-lived */
 
 /*