On Thu, 2013-07-18 at 18:07 +0900, 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 us > > Hello, > I have a question :) > > So, each contention takes 7.6 ms in your result. Well, that's the total wait time. I can see your concern, but no, things aren't *that* bad. The average amount of time spent waiting for the lock would be 76888911.01/10678 = 7200us > 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'm wondering why it takes so long. > I cannot really say. This is proprietary software. AFAICT if Oracle is anything like Posgres, than probably no. > And do you use 16KB-size hugepage? No, 2Mb pages. > 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. Thanks, Davidlohr -- 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>