severely bloated slabs

severely bloated slabs

[William Lee Irwin III]

12 hours after running dbench, tiobench, and a couple of others:

             cache      active    alloc    %util
       buffer_head:     3781KB   132278KB    2.85
         pte_chain:       46KB      520KB    8.98
      dentry_cache:     8256KB    47662KB   17.32
    vm_area_struct:      226KB      817KB   27.75
               bio:       98KB      295KB   33.26
          biovec-1:       25KB       75KB   33.45
           size-32:      377KB     1098KB   34.38
           size-64:      251KB      700KB   35.93
  proc_inode_cache:      517KB     1157KB   44.74
       task_struct:      788KB     1697KB   46.47
         size-4096:     2480KB     5240KB   47.32
        signal_act:      688KB     1379KB   49.86
 skbuff_head_cache:      384KB      738KB   52.3 
          tcp_sock:      465KB      767KB   60.63
   radix_tree_node:     9533KB    14851KB   64.18
       files_cache:      487KB      677KB   71.96
  sock_inode_cache:      248KB      341KB   72.74
          sgpool-8:      195KB      255KB   76.83
         size-2048:     1132KB     1372KB   82.50
          size-256:      606KB      701KB   86.52
  tcp_open_request:       54KB       62KB   87.43


132MB of ZONE_NORMAL on a 16GB i386 box tied up in buffer_head slabs
when all of 3% of it is in use gives me the willies. Periodic slab
pruning anyone? Might be useful in addition to slab-in-lru.


Cheers,
Bill
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Re: severely bloated slabs

[Martin J. Bligh]

> 132MB of ZONE_NORMAL on a 16GB i386 box tied up in buffer_head slabs
> when all of 3% of it is in use gives me the willies. Periodic slab
> pruning anyone? Might be useful in addition to slab-in-lru.

As long as we give this up under memory pressure, why does this
matter?

M.

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Re: severely bloated slabs

[William Lee Irwin III]

At some point in the past, I wrote:
>> 132MB of ZONE_NORMAL on a 16GB i386 box tied up in buffer_head slabs
>> when all of 3% of it is in use gives me the willies. Periodic slab
>> pruning anyone? Might be useful in addition to slab-in-lru.

On Tue, Jul 30, 2002 at 10:39:35AM -0700, Martin J. Bligh wrote:
> As long as we give this up under memory pressure, why does this
> matter?

Mostly a question of response time and long idle times being a good
indicator of upcoming workload shifts. I'd say it's behaving as
designed, but not as desired.


Cheers,
Bill
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Re: severely bloated slabs

[Ed Tomlinson]

On July 30, 2002 01:53 pm, William Lee Irwin III wrote:
> At some point in the past, I wrote:
> >> 132MB of ZONE_NORMAL on a 16GB i386 box tied up in buffer_head slabs
> >> when all of 3% of it is in use gives me the willies. Periodic slab
> >> pruning anyone? Might be useful in addition to slab-in-lru.
>
> On Tue, Jul 30, 2002 at 10:39:35AM -0700, Martin J. Bligh wrote:
> > As long as we give this up under memory pressure, why does this
> > matter?
>
> Mostly a question of response time and long idle times being a good
> indicator of upcoming workload shifts. I'd say it's behaving as
> designed, but not as desired.

Was this with full rmap + slablru or with a linus kernel?  With slablru
I would expect this to happen to some extent.  When vm pressure picks
up slablru is fast to free the 'old' slabs...  On the other hand, if periodic
prunes are really a good idea, it would be easy to have slablru do them
for us.  As it stands now, slablru adds a flag bit to each slab cache telling
slablru to prune the cache instead of just the page encounted.  This flag
gets set when we are able to add a page to the lru (when the pagemap_lru
lock is busy).  I would not be hard to set this flag under other conditions.

Ed
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Re: severely bloated slabs

[William Lee Irwin III]

On July 30, 2002 01:53 pm, William Lee Irwin III wrote:
>> Mostly a question of response time and long idle times being a good
>> indicator of upcoming workload shifts. I'd say it's behaving as
>> designed, but not as desired.

On Tue, Jul 30, 2002 at 08:13:01PM -0400, Ed Tomlinson wrote:
> Was this with full rmap + slablru or with a linus kernel?  With slablru
> I would expect this to happen to some extent.  When vm pressure picks
> up slablru is fast to free the 'old' slabs...  On the other hand, if periodic
> prunes are really a good idea, it would be easy to have slablru do them
> for us.  As it stands now, slablru adds a flag bit to each slab cache telling
> slablru to prune the cache instead of just the page encounted.  This flag
> gets set when we are able to add a page to the lru (when the pagemap_lru
> lock is busy).  I would not be hard to set this flag under other conditions.

Sounds reasonable, not sure what the general consensus is on periodic
prunes, though. I'm mostly thinking of the desktop workload for this
one, as servers are probably not going to really care. But I'm not a good
testcase for this one as even my "desktop" usage patterns are atypical.


Cheers,
Bill
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