Re: [RFC][PATCH] dcache and rmap

[Ed Tomlinson <tomlins@cam.org>]

Hi,

I did something similiar in the patch I posted under the subject:

[RFC][PATCH] cache shrinking via page age

Only I used the same method we now use to shrink caches but triggered them
using page aging, and at the same time making the trigger cache specific.

Another though I had was to put the 'freeable' slab pages onto the inactive
clean list and reclaim them when they reach the head of the list.  It gets a 
little tricky since slabs can contain multiple pages...   Before trying this
I want to see how well what I have posted works.

Ed Tomlinson

On May 13, 2002 07:07 am, Nikita Danilov wrote:
> William Lee Irwin III writes:
>  > At some point in the past, I wrote:
>  > >> In short, I don't think you went far enough. How do you feel about
>  > >> GFP_SPECULATIVE (a.k.a. GFP_DONT_TRY_TOO_HARD), cache priorities and
>  > >> cache shrinking drivers?
>  >
>  > On Tue, May 07, 2002 at 07:41:52AM -0400, Ed Tomlinson wrote:
>  > > Think I will sprinkle slab.c with a printk or two to see if we detect
>  > > when it's allocations are eating other caches.  If this works we
>  > > should be able to let the vm know when to shrink the slab cache and to
>  > > let it know which caches need shrinking (ie shrink_caches becomes a
>  > > 'driver' to shrink the dcache/icache family.  kmem_cache_reap being
>  > > the generic 'driver') Thanks for the feedback and interesting idea,
>  >
>  > Well, the trick is kmem_cache_reap() doesn't know how to prune
>  > references to things within the cache like prune_dcache() does. It is
>  > in essence its own cache in front of another cache for allocations. I'm
>  > not sure making kmem_cache_reap() trigger reaping of the caches it's
>  > parked in front of is a great idea. It seems that it would go the other
>  > direction: reaping a cache parked in front of a slab would want to call
>  > kmem_cache_reap() sometime afterward (so the memory is actually
>  > reclaimed instead of sitting in the slab cache). IIRC the VM actually
>  > does this at some point after calling the assorted cache shrink
>  > functions. kmem_cache_reap() may well be needed in contexts where the
>  > caches are doing fine jobs of keeping their space under control or
>  > shrinking themselves just fine, without intervention from outside
>  > callers.
>
> I remember Linus once mentioned an idea that slab pages should have
> ->writepage() that triggers shrink of the front-end cache.
>
> Along this way, VM would just manage one big cache---physical memory.
>
>  > Cheers,
>  > Bill
>
> Nikita.

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