On Mon, 9 Jul 2007 10:26:08 -0700 (PDT) Christoph Lameter <[EMAIL PROTECTED]> wrote:
> > I assume the tradeoff here is better packing versus having a ridiculous > > number of caches. Is there any other cost? > > Because even having 1024 caches wouldn't consume a terrible amount of > > memory and I bet it would result in aggregate savings. > > I have tried any number of approaches without too much success. Even one > slab cache for every 8 bytes. This creates additional admin overhead > through more control structure (that is pretty minimal but nevertheless > exists) > > The main issue is that kmallocs of different size must use different > pages. If one allocates one 64 byte item and one 256 byte item and both 64 > byte and 256 byte are empty then SLAB/SLUB will have to allocate 2 pages. > SLUB can fit them into one. This is basically only relevant early after > boot. The advantage goes away as the system starts to work and as more > objects are allocated in the slabs but the power-of-two slab will always > have to extend its size in page size chunks which leads to some overhead > that SLOB can avoid by placing entities of multiple size in one slab. > The tradeoff in SLOB is that is cannot be an O(1) allocator because it > has to manage these variable sized objects by traversing the lists. > > I think the advantage that SLOB generates here is pretty minimal and is > easily offset by the problems of maintaining SLOB. Sure. But I wasn't proposing this as a way to make slub cover slob's advantage. I was wondering what effect it would have on a more typical medium to large sized system. Not much, really: if any particular subsystem is using a "lot" of slab memory then it should create its own cache rather than using kmalloc anyway, so forget it ;) - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
