Hello,
> On Tue, Oct 19, 2010 at 02:42:47PM +1100, npiggin@xxxxxxxxx wrote:
> > Per-zone LRUs and shrinkers for inode cache.
>
> Regardless of whether this is the right way to scale or not, I don't
> like the fact that this moves the cache LRUs into the memory
> management structures, and expands the use of MM specific structures
> throughout the code. It ties the cache implementation to the current
> VM implementation. That, IMO, goes against all the principle of
> modularisation at the source code level, and it means we have to tie
> all shrinker implemenations to the current internal implementation
> of the VM. I don't think that is wise thing to do because of the
> dependencies and impedance mismatches it introduces.
>
> As an example: XFS inodes to be reclaimed are simply tagged in a
> radix tree so the shrinker can reclaim inodes in optimal IO order
> rather strict LRU order. It simply does not match a zone-based
> shrinker implementation in any way, shape or form, nor does it's
> inherent parallelism match that of the way shrinkers are called.
>
> Any change in shrinker infrastructure needs to be able to handle
> these sorts of impedance mismatches between the VM and the cache
> subsystem. The current API doesn't handle this very well, either,
> so it's something that we need to fix so that scalability is easy
> for everyone.
>
> Anyway, my main point is that tying the LRU and shrinker scaling to
> the implementation of the VM is a one-off solution that doesn't work
> for generic infrastructure. Other subsystems need the same
> large-machine scaling treatment, and there's no way we should be
> tying them all into the struct zone. It needs further abstraction.
I'm not sure what data structure is best. I can only say current
zone unawareness slab shrinker might makes following sad scenario.
o DMA zone shortage invoke and plenty icache in NORMAL zone dropping
o NUMA aware system enable zone_reclaim_mode, but shrink_slab() still
drop unrelated zone's icache
both makes performance degression. In other words, Linux does not have
flat memory model. so, I don't think Nick's basic concept is wrong.
It's straight forward enhancement. but if it don't fit current shrinkers,
I'd like to discuss how to make better data structure.
and I have dump question (sorry, I don't know xfs at all). current
xfs_mount is below.
typedef struct xfs_mount {
...
struct shrinker m_inode_shrink; /* inode reclaim shrinker */
} xfs_mount_t;
Do you mean xfs can't convert shrinker to shrinker[ZONES]? If so, why?
Thanks.
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