Messages in this thread | | | Date | Tue, 16 Jul 2013 11:12:45 +0900 | From | Joonsoo Kim <> | Subject | Re: [PATCH 7/9] mm, hugetlb: add VM_NORESERVE check in vma_has_reserves() |
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On Mon, Jul 15, 2013 at 08:41:12PM +0530, Aneesh Kumar K.V wrote: > Joonsoo Kim <iamjoonsoo.kim@lge.com> writes: > > > If we map the region with MAP_NORESERVE and MAP_SHARED, > > we can skip to check reserve counting and eventually we cannot be ensured > > to allocate a huge page in fault time. > > With following example code, you can easily find this situation. > > > > Assume 2MB, nr_hugepages = 100 > > > > fd = hugetlbfs_unlinked_fd(); > > if (fd < 0) > > return 1; > > > > size = 200 * MB; > > flag = MAP_SHARED; > > p = mmap(NULL, size, PROT_READ|PROT_WRITE, flag, fd, 0); > > if (p == MAP_FAILED) { > > fprintf(stderr, "mmap() failed: %s\n", strerror(errno)); > > return -1; > > } > > > > size = 2 * MB; > > flag = MAP_ANONYMOUS | MAP_SHARED | MAP_HUGETLB | MAP_NORESERVE; > > p = mmap(NULL, size, PROT_READ|PROT_WRITE, flag, -1, 0); > > if (p == MAP_FAILED) { > > fprintf(stderr, "mmap() failed: %s\n", strerror(errno)); > > } > > p[0] = '0'; > > sleep(10); > > > > During executing sleep(10), run 'cat /proc/meminfo' on another process. > > You'll find a mentioned problem. > > > > Solution is simple. We should check VM_NORESERVE in vma_has_reserves(). > > This prevent to use a pre-allocated huge page if free count is under > > the reserve count. > > You have a problem with this patch, which i guess you are fixing in > patch 9. Consider two process > > a) MAP_SHARED on fd > b) MAP_SHARED | MAP_NORESERVE on fd > > We should allow the (b) to access the page even if VM_NORESERVE is set > and we are out of reserve space .
I can't get your point. Please elaborate more on this.
Thanks.
> > so may be you should rearrange the patch ? > > > > > Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com> > > > > diff --git a/mm/hugetlb.c b/mm/hugetlb.c > > index 6c1eb9b..f6a7a4e 100644 > > --- a/mm/hugetlb.c > > +++ b/mm/hugetlb.c > > @@ -464,6 +464,8 @@ void reset_vma_resv_huge_pages(struct vm_area_struct *vma) > > /* Returns true if the VMA has associated reserve pages */ > > static int vma_has_reserves(struct vm_area_struct *vma) > > { > > + if (vma->vm_flags & VM_NORESERVE) > > + return 0; > > if (vma->vm_flags & VM_MAYSHARE) > > return 1; > > if (is_vma_resv_set(vma, HPAGE_RESV_OWNER)) > > -- > > 1.7.9.5 > > -- > 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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