Re: [PATCH v6 12/31] fs: convert inode and dentry shrinking to be node aware

[Glauber Costa <glommer@parallels.com>]

On 05/17/2013 06:49 PM, Glauber Costa wrote:
> On 05/17/2013 11:29 AM, Glauber Costa wrote:
>> Except that shrink_slab_node would also defer work, right?
>>
>>>> The only thing I don't like about this is the extra nodemask needed,
>>>> which, like the scan control, would have to sit on the stack.
>>>> Suggestions for avoiding that problem are welcome.. :)
>>>>
>> I will try to come up with a patch to do all this, and then we can
>> concretely discuss.
>> You are also of course welcome to do so as well =)
> 
> 
> All right.
> 
> I played a bit today with variations of this patch that will keep the
> deferred count per node. I will rebase the whole series ontop of it (the
> changes can get quite disruptive) and post. I want to believe that
> after this, all our regression problems will be gone (famous last words).
> 
> As I have told you, I wasn't seeing problems like you are, and
> speculated that this was due to the disk speeds. While this is true,
> the patch I came up with makes my workload actually a lot better.
> While my caches weren't being emptied, they were being slightly depleted
> and then slowly filled again. With my new patch, it is almost
> a straight line throughout the whole find run. There is a dent here and
> there eventually, but it recovers quickly. It takes some time as well
> for steady state to be reached, but once it is, we have all variables
> in the equation (dentries, inodes, etc) basically flat. So I guess it
> works, and I am confident that it will make your workload better.
> 
> My strategy is to modify the shrinker structure like this:
> 
> struct shrinker {
>         int (*shrink)(struct shrinker *, struct shrink_control *sc);
>         long (*count_objects)(struct shrinker *, struct shrink_control *sc);
>         long (*scan_objects)(struct shrinker *, struct shrink_control *sc);
> 
>         int seeks;      /* seeks to recreate an obj */
>         long batch;     /* reclaim batch size, 0 = default */
>         unsigned long flags;
> 
>         /* These are for internal use */
>         struct list_head list;
>         atomic_long_t *nr_deferred; /* objs pending delete, per node */
> 
>         /* nodes being currently shrunk, only makes sense for NUMA
> shrinkers */
>         nodemask_t *nodes_shrinking;
> 
> };
> 
> We need memory allocation now for nr_deferred and nodes_shrinking, but
> OTOH we use no stack, and can keep the size of this to be dynamically
> adjusted depending on whether or not your shrinker is NUMA aware.
> 
> Guess that is it. Expect news soon.
> 

Except of course that struct shrinker is obviously shared between runs,
and this won't cut.

Right now I am inclined to really just put this in the stack. The
alternative, if it becomes a problem, can be to extend the lru apis
to allow us to go for a single node. This way we only need to use 1
extra word in the stack.

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