On Fri, 6 Apr 2007 10:01:38 -0700 (PDT) Christoph Lameter <[EMAIL PROTECTED]> wrote:
> On Thu, 5 Apr 2007, Andrew Morton wrote: > > > > We add PageTail as an alias of PageReclaim. Compound pages cannot > > > currently be reclaimed. Because of the alias one needs to check > > > PageCompound first. > > > > So slub is using compound pages so that it can locate the head page in > > higher-order pages, whereas slab uses per-object (or per-order-0-page?) > > metadata for that? > > Both SLAB and SLUB use compound pages. Not really. slab sets the page->lru.prev of each constituent page to point at the controlling slab. I assume the PageCompound() handling in (for example) page_get_cache() is for the NOMMU special case. > > > > I see four instances of > > > > + page = virt_to_page(p); > > + > > + if (unlikely(PageCompound(page))) > > + page = page->first_page; > > > > A new virt_to_head_page() is needed. > > Ok. > > > Sigh. We're seeing rather a lot of churn to accommodate slub. Do we > > actually have any justification for all this? If we end up deciding to > > merge slub and to deprecate then remove slab, what would our reasons have > > been? > > This is not SLUB specific. SLAB does the same. SLAB does special casing > for page size slabs and does not allow slab debugging because it would > use page->private if debugging would be enabled. Which would get into > trouble on i386. > > If you want less SLUB churn on other fronts then I can add the special > casing for PAGE_SIZE slabs back into SLUB. Then we keep all the > inconsistencies in SLAB use in the code. > > I'd rather clean up the stuff and then also remove the special casing from > SLAB. > Will slub handle NOMMU anonymous pages appropriately? - 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/
