On Mon, 27 Feb 2012 23:00:28 -0500 Steven Truelove <steven.truelove@xxxxxxxxxxx> wrote: > When calling shmget() with SHM_HUGETLB, shmget aligns the request size to PAGE_SIZE, but this is not sufficient. Modified hugetlb_file_setup() to align requests to the huge page size. Also modified mmap_pgoff() to avoid duplicating this check and to align against the start address. > I don't think this is quite right. Suppose huge_page_size is 4096, addr=4095, len=4098. So we're mapping three pages: the last byte of the first page, all of the second page and the first byte of the third page. > --- a/fs/hugetlbfs/inode.c > +++ b/fs/hugetlbfs/inode.c > @@ -938,6 +938,8 @@ struct file *hugetlb_file_setup(const char *name, size_t size, > struct path path; > struct dentry *root; > struct qstr quick_string; > + struct hstate *hstate; > + int num_pages; > > *user = NULL; > if (!hugetlbfs_vfsmount) > @@ -967,10 +969,11 @@ struct file *hugetlb_file_setup(const char *name, size_t size, > if (!inode) > goto out_dentry; > > + hstate = hstate_inode(inode); > + num_pages = ALIGN(size, huge_page_size(hstate)) >> > + huge_page_shift(hstate); > error = -ENOMEM; > - if (hugetlb_reserve_pages(inode, 0, > - size >> huge_page_shift(hstate_inode(inode)), NULL, > - acctflag)) > + if (hugetlb_reserve_pages(inode, 0, num_pages, NULL, acctflag)) > goto out_inode; > > d_instantiate(path.dentry, inode); > diff --git a/mm/mmap.c b/mm/mmap.c > index 3f758c7..1f44ccf 100644 > --- a/mm/mmap.c > +++ b/mm/mmap.c > @@ -1098,8 +1098,12 @@ SYSCALL_DEFINE6(mmap_pgoff, unsigned long, addr, unsigned long, len, > * taken when vm_ops->mmap() is called > * A dummy user value is used because we are not locking > * memory so no accounting is necessary > + * Length is increased by the amount necessary to align > + * the base address to the huge page size. > + * hugetlb_file_setup() aligns the end of the buffer to > + * the huge page size. > */ > - len = ALIGN(len, huge_page_size(&default_hstate)); > + len += ALIGN(addr, huge_page_size(&default_hstate)) - addr; > file = hugetlb_file_setup(HUGETLB_ANON_FILE, len, VM_NORESERVE, > &user, HUGETLB_ANONHUGE_INODE); mmap_pgoff() will change `len' from 4098 to 4099. hugetlb_file_setup() will round that up to 8192 and will decide to reserve two pages, not three. -- 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>