On Thu, 2013-07-18 at 17:19 -0700, Davidlohr Bueso wrote: > 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.bu...@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. > > 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 >
Long day, I think this is what you were saying for the start :) > > 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 from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
