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@xxxxxx> - 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 usHello, 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@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
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