Re: [Lsf-pc] [LSF/MM TOPIC] slab reclaim

[Jan Kara <jack@suse.cz>]

Hi!

On Wed 28-12-16 14:09:51, Michal Hocko wrote:
> I would like to propose the following for LSF/MM discussion. Both MM and
> FS people should be involved.
> 
> The current way of the slab reclaim is rather suboptimal from 2
> perspectives.
> 
> 1) The slab allocator relies on shrinkers to release pages but shrinkers
> are object rather than page based. This means that the memory reclaim
> asks to free some pages, slab asks shrinkers to free some objects
> and the result might be that nothing really gets freed even though
> shrinkers do their jobs properly because some objects are still pinning
> the page. This is not a new problem and it has been discussed in the
> past. Dave Chinner has even suggested a solution [1] which sounds like
> the right approach. There was no follow up and I believe we should
> into implementing it.
> 
> 2) The way we scale slab reclaim pressure depends on the regular LRU
> reclaim. There are workloads which do not general a lot of pages on LRUs
> while they still consume a lot of slab memory. We can end up even going
> OOM because the slab reclaim doesn't free up enough. I am not really
> sure how the proper solution should look like but either we need some
> way of slab consumption throttling or we need a more clever slab
> pressure estimation.
> 
> [1] https://lkml.org/lkml/2010/2/8/329.

I'm interested in this topic although I think it currently needs more
coding and experimenting than discussions...

								Honza
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR

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