Trying to use SLUB in an odd way

From: Charles Manning
Date: Sun May 23 2010 - 22:46:39 EST


YAFFS uses an internal almost slub-like allocator and I've been looking at
moving it to use SLUB as part of an attempt to mainline yaffs.

In yaffs I create a lot of tiny objects which are allocated in blocks, like
slub, and then managed in a free list. Very slubbish so far, but mine is far
less intelligent than slub.

The difference though is that I can keep the objects for each mount separate
and can dump the whole lot on umount without individually freeing objects. I
just deallocate my whole cache.

There are two problems that I encountered in moving to slub:
1) I want to keep each mount point separate, but slub just hooks up with an
existing cache of the same size. I managed to trick slub into keeping yaffs
objects in their own cache by assigning a fake ctor. That stops the
combination (well at present anyway - could easy change in the future like if
ctor gets dropped). Like a VW Bug: ugly but it gets you there....

2) If I dump a cache with existing in-use objects then slub gets upset and
dumps warnings. I don't like the idea of just ignoring warnings. I also don't
want to manually tear down trees etc when the existing "just dump it"
approach is a lot faster. Pity there is no "trust me I know what I'm doing"

A) Is there a better way to use slub to do this or is it better to just
continue with my manual allocator?

B) Is it worth adding flags to kmem_cache_create() to say:
a) Don't combine this slub with others.
b) "Trust me I know what I'm doing": Allow the cache to be dumped with
objects still allocated.

If (B) makes sense I'll put together a patch.

-- Charles

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