lkml.org 
[lkml]   [2006]   [Dec]   [25]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH 6/6] containers: BeanCounters over generic process containers
Herbert Poetzl wrote:
> On Fri, Dec 22, 2006 at 06:14:48AM -0800, Paul Menage wrote:
>> This patch implements the BeanCounter resource control abstraction
>> over generic process containers. It contains the beancounter core
>> code, plus the numfiles resource counter. It doesn't currently contain
>> any of the memory tracking code or the code for switching beancounter
>> context in interrupts.
>
> I don't like it, it looks bloated and probably
> adds plenty of overhead (similar to the OVZ
> implementation where this seems to be taken from)

FULL BC patch w/o pages fractions accounting doesn't
add any noticeable overhead to mainstream kernel.
Pages fractions accounting will be optimized as well.
The part you're talking about is only 1/100 of the
complete patch.

> here are some comments/questions:
>
>> Currently all the beancounters resource counters are lumped into a
>> single hierarchy; ideally it would be possible for each resource
>> counter to be a separate container subsystem, allowing them to be
>> connected to different hierarchies.
>>
>> +static inline void bc_uncharge(struct beancounter *bc, int res_id,
>> + unsigned long val)
>> +{
>> + unsigned long flags;
>> +
>> + spin_lock_irqsave(&bc->bc_lock, flags);
>> + bc_uncharge_locked(bc, res_id, val);
>> + spin_unlock_irqrestore(&bc->bc_lock, flags);
>
> why use a spinlock, when we could use atomic
> counters?

Because approach

if (atomic_read(&bc->barrier) > aromic_read(&bc->held))
atomic_inc(&bc->held);
used in vserver accounting is not atomic ;)

Look at the comment below about charging two resources at once.

>
>> +int bc_charge_locked(struct beancounter *bc, int res, unsigned long val,
>> + int strict, unsigned long flags)
>> +{
>> + struct bc_resource_parm *parm;
>> + unsigned long new_held;
>> +
>> + BUG_ON(val > BC_MAXVALUE);
>> +
>> + parm = &bc->bc_parms[res];
>> + new_held = parm->held + val;
>> +
>> + switch (strict) {
>> + case BC_LIMIT:
>> + if (new_held > parm->limit)
>> + break;
>> + /* fallthrough */
>> + case BC_BARRIER:
>> + if (new_held > parm->barrier) {
>> + if (strict == BC_BARRIER)
>> + break;
>> + if (parm->held < parm->barrier &&
>> + bc_resources[res]->bcr_barrier_hit)
>> + bc_resources[res]->bcr_barrier_hit(bc);
>> + }
>
> why do barrier checks with every accounting?
> there are probably a few cases where the
> checks could be independant from the accounting

Let's look at

if (parm->held < parm->barrier &&
bc_resources[res]->bcr_barrier_hit)
bc_resources[res]->bcr_barrier_hit(bc);
code one more time.

In case of BC_LIMIT charge BC code informs resource
controller about BARRIER hit to take some actions
before hard resource shortage.

>> + /* fallthrough */
>> + case BC_FORCE:
>> + parm->held = new_held;
>> + bc_adjust_maxheld(parm);
>
> in what cases do we want to cross the barrier?
>
>> + return 0;
>> + default:
>> + BUG();
>> + }
>> +
>> + if (bc_resources[res]->bcr_limit_hit)
>> + return bc_resources[res]->bcr_limit_hit(bc, val, flags);
>> +
>> + parm->failcnt++;
>> + return -ENOMEM;
>
>> +int bc_file_charge(struct file *file)
>> +{
>> + int sev;
>> + struct beancounter *bc;
>> +
>> + task_lock(current);
>
> why do we lock current? it won't go away that
> easily, and for switching the bc, it might be
> better to use RCU or a separate lock, no?

This came from containers patches. BC code doesn't take
locks on fast paths.

>> + bc = task_bc(current);
>> + css_get_current(&bc->css);
>> + task_unlock(current);
>> +
>> + sev = (capable(CAP_SYS_ADMIN) ? BC_LIMIT : BC_BARRIER);
>> +
>> + if (bc_charge(bc, BC_NUMFILES, 1, sev)) {
>> + css_put(&bc->css);
>> + return -EMFILE;
>> + }
>> +
>> + file->f_bc = bc;
>> + return 0;
>> +}
>
> also note that certain limits are much more
> complicated than the (very simple) file limits
> and the code will be called at higher frequency

We do know it and we have "pre-charges" optimization
for frequent calls. bc->lock we've seen is used to
make two or more resources charge in only one atomic
operation, that is faster than doing atomic_inc()
for each resource as you've proposed above.

> how to handle requests like:
> try to get as 64 files or as many as available
> whatever is smaller

I promise, that if Linus will include patch that adds a syscall
to open 64 or "as many as available whatever is smaller" files
at once we'll add this functionality.

> happy xmas,
> Herbert
>
>

-
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: 2006-12-25 11:41    [from the cache]
©2003-2011 Jasper Spaans