Messages in this thread | | | Date | Tue, 23 Jul 2013 15:04:54 +0800 | From | Hush Bensen <> | Subject | Re: [PATCH] hugepage: allow parallelization of the hugepage fault path |
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On 07/18/2013 05:07 PM, Joonsoo Kim wrote: > On Wed, Jul 17, 2013 at 12:50:25PM -0700, Davidlohr Bueso wrote: > >> From: Davidlohr Bueso <davidlohr.bueso@hp.com> >> >> - Cleaned up and forward ported to Linus' latest. >> - Cache aligned mutexes. >> - Keep non SMP systems using a single mutex. >> >> It was found that this mutex can become quite contended >> during the early phases of large databases which make use of huge pages - for instance >> startup and initial runs. One clear example is a 1.5Gb Oracle database, where lockstat >> reports that this mutex can be one of the top 5 most contended locks in the kernel during >> the first few minutes: >> >> hugetlb_instantiation_mutex: 10678 10678 >> --------------------------- >> hugetlb_instantiation_mutex 10678 [<ffffffff8115e14e>] hugetlb_fault+0x9e/0x340 >> --------------------------- >> hugetlb_instantiation_mutex 10678 [<ffffffff8115e14e>] hugetlb_fault+0x9e/0x340 >> >> contentions: 10678 >> acquisitions: 99476 >> waittime-total: 76888911.01 us > Hello, > I have a question :) > > So, each contention takes 7.6 ms in your result. > Do you map this area with VM_NORESERVE? > If we map with VM_RESERVE, when page fault, we just dequeue a huge page from a queue and clear > a page and then map it to a page table. So I guess, it shouldn't take so long.
I don't think there is clear page operation after dequeue huge page, actually it's even not done during hugetlb_reserve_pages, do you know why? There is just clear operation in hugetlb_no_page.
> I'm wondering why it takes so long. > > And do you use 16KB-size hugepage? > If so, region handling could takes some times. If you access the area as random order, > the number of region can be more than 90000. I guess, this can be one reason to too long > waittime. > > Thanks. > > -- > To unsubscribe, send a message with 'unsubscribe linux-mm' in > the body to majordomo@kvack.org. For more info on Linux MM, > see: http://www.linux-mm.org/ . > Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
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