Messages in this thread | | | Date | Tue, 9 Mar 2004 00:08:45 +0100 | From | Andrea Arcangeli <> | Subject | Re: objrmap-core-1 (rmap removal for file mappings to avoid 4:4 in <=16G machines) |
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On Mon, Mar 08, 2004 at 10:28:38PM +0100, Arjan van de Ven wrote: > > . Basically without > > this fix it's like 2.6 is running w/o pte-highmem. 700 tasks with 2.7G > > of shm mapped each would run the box out of zone-normal even with 4:4. > > With 3:1 100 tasks would be enough. Math is easy: > > > > 2.7*1024*1024*1024/4096*8*100/1024/1024/1024 > > 2.7*1024*1024*1024/4096*8*700/1024/1024/1024 > > > not saying your patch is not useful or anything,but there is a less > invasive shortcut possible. Oracle wants to mlock() its shared area, and > for mlock()'d pages we don't need a pte chain *at all*. So we could get > rid of a lot of this overhead that way.
I agree that works fine for Oracle, that's becase Oracle is an extreme special case since most of this shared memory is an I/O cache, this is not the case of other apps, and those other apps really depends on the kernel vm paging algorithms for things more than istantiating a pte (or a pmd if it's a largepage). Other apps can't use mlock. Some of these apps works closely with oracle too.
dropping pte_chains through mlock was suggested around april 2003 originally by Wli and I didn't like that idea since we really want to allow swapping if we run short of ram. And it doesn't solve the scalability slowdown on the 32-way for kernel compiles either. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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