lkml.org 
[lkml]   [2007]   [May]   [5]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [RFC 0/3] Slab Defrag / Slab Targeted Reclaim and general Slab API changes
Eric Dumazet a écrit :
> Christoph Lameter a écrit :
>
>>
>>> G. Being able to track the number of pages in a kmem_cache
>>>
>>>
>>> If you look at fs/buffer.c, you'll notice the bh_accounting,
>>> recalc_bh_state()
>>> that might be overkill for large SMP configurations, when the real
>>> concern is
>>> to be able to limit the bh's not to exceed 10% of LOWMEM.
>>>
>>> Adding a callback in slab_ops to track total number of pages in use
>>> by a given
>>> kmem_cache would be good.
>>
>> Such functionality exists internal to SLUB and in the reporting tool.
>> I can export that function if you need it.
>>
>>> Same thing for fs/file_table.c : nr_file logic
>>> (percpu_counter_dec()/percpu_counter_inc() for each file open/close)
>>> could be
>>> simplified if we could just count the pages in use by filp_cachep
>>> kmem_cache.
>>> The get_nr_files() thing is not worth the pain.
>>
>> Sure. What exactly do you want? The absolute number of pages of memory
>> that the slab is using?
>>
>> kmem_cache_pages_in_use(struct kmem_cache *) ?
>>
>> The call will not be too lightweight since we will have to loop over
>> all nodes and add the counters in each per node struct for allocates
>> slabs.
>>
>>
>
> On a typical system, number of pages for 'filp' kmem_cache tends to be
> stable
>
> -bash-2.05b# grep filp /proc/slabinfo
> filp 234727 374100 256 15 1 : tunables 120 60
> 8 : slabdata 24940 24940 135
> -bash-2.05b# grep filp /proc/slabinfo
> filp 234776 374100 256 15 1 : tunables 120 60
> 8 : slabdata 24940 24940 168
> -bash-2.05b# grep filp /proc/slabinfo
> filp 234728 374100 256 15 1 : tunables 120 60
> 8 : slabdata 24940 24940 180
> -bash-2.05b# grep filp /proc/slabinfo
> filp 234724 374100 256 15 1 : tunables 120 60
> 8 : slabdata 24940 24940 174
>
> So revert nr_files logic to a single integer would be enough, even for NUMA
>
> int nr_pages_used_by_filp;
> int nr_pages_filp_limit;
> int filp_in_danger __read_mostly;
>
> static void callback_pages_in_use_by_filp(int inc)
> {
> int in_danger;
>
> nr_pages_used_by_filp += inc;
>
> in_danger = nr_pages_used_by_filp >= nr_pages_filp_limit;
> if (in_danger != filp_in_danger)
> filp_in_danger = in_danger;
> }
>
> struct file *get_empty_filp(void)
> {
> ...
> if (filp_in_danger && !capable(CAP_SYS_ADMIN))
> goto over;
>
> ...
> }
>
>
> void __init files_init(unsigned long mempages)
> {
> ...
> nr_pages_filp_limit = (mempages * 10) / 100; /* 10% for filp use */
> ...
> }


This wont work of course : Once the pages limit is hit, file allocations would
be forbidden until cache is shrinked.

Maybe callback should return a status, so that SLAB / SLUB can return ENOMEM

static int callback_pages_in_use_by_filp(int inc)
{
int in_danger;

nr_pages_used_by_filp += inc;

in_danger = nr_pages_used_by_filp >= nr_pages_filp_limit;
if (unlikely(in_danger != filp_in_danger))
filp_in_danger = in_danger;
if (unlikely(in_danger && inc > 0 && !capable(CAP_SYS_ADMIN))) {
nr_pages_used_by_filp -= inc;
return -1;
}
return 0;
}

No more tests in get_empty_filp() : just call kmem_cache_alloc()

struct file *get_empty_filp(void)
{
...
f = kmem_cache_alloc(filp_cachep, GFP_KERNEL);
...
}

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2007-05-05 09:41    [W:0.026 / U:33.896 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site