On Mon, 5 Nov 2012 15:24:08 -0800
Andi Kleen <andi@xxxxxxxxxxxxxx> wrote:
> From: Andi Kleen <ak@xxxxxxxxxxxxxxx>
>
> There was some desire in large applications using MAP_HUGETLB/SHM_HUGETLB
> to use 1GB huge pages on some mappings, and stay with 2MB on others. This
> is useful together with NUMA policy: use 2MB interleaving on some mappings,
> but 1GB on local mappings.
>
> This patch extends the IPC/SHM syscall interfaces slightly to allow specifying
> the page size.
>
> It borrows some upper bits in the existing flag arguments and allows encoding
> the log of the desired page size in addition to the *_HUGETLB flag.
> When 0 is specified the default size is used, this makes the change fully
> compatible.
>
> Extending the internal hugetlb code to handle this is straight forward. Instead
> of a single mount it just keeps an array of them and selects the right
> mount based on the specified page size. When no page size is specified
> it uses the mount of the default page size.
>
> The change is not visible in /proc/mounts because internal mounts
> don't appear there. It also has very little overhead: the additional
> mounts just consume a super block, but not more memory when not used.
>
> I also exported the new flags to the user headers
> (they were previously under __KERNEL__). Right now only symbols
> for x86 and some other architecture for 1GB and 2MB are defined.
> The interface should already work for all other architectures
> though. Only architectures that define multiple hugetlb sizes
> actually need it (that is currently x86, tile, powerpc). However
> tile and powerpc have user configurable hugetlb sizes, so it's
> not easy to add defines. A program on those architectures would
> need to query sysfs and use the appropiate log2.
I can't say the userspace interface is a thing of beauty, but I guess
we'll live.
Did you have a test app? If so, can we get it into
tools/testing/selftests and point the arch maintainers at it?
>
> ...
>
> @@ -1011,8 +1029,9 @@ out_shm_unlock:
>
> static int __init init_hugetlbfs_fs(void)
> {
> + struct hstate *h;
> int error;
> - struct vfsmount *vfsmount;
> + int i;
>
> error = bdi_init(&hugetlbfs_backing_dev_info);
> if (error)
> @@ -1029,14 +1048,27 @@ static int __init init_hugetlbfs_fs(void)
> if (error)
> goto out;
>
> - vfsmount = kern_mount(&hugetlbfs_fs_type);
> -
> - if (!IS_ERR(vfsmount)) {
> - hugetlbfs_vfsmount = vfsmount;
> - return 0;
> + i = 0;
> + for_each_hstate (h) {
> + char buf[50];
> + unsigned ps_kb = 1U << (h->order + PAGE_SHIFT - 10);
> +
> + snprintf(buf, sizeof buf, "pagesize=%uK", ps_kb);
> + hugetlbfs_vfsmount[i] = kern_mount_data(&hugetlbfs_fs_type,
> + buf);
> +
> + if (IS_ERR(hugetlbfs_vfsmount[i])) {
> + pr_err(
> + "hugetlb: Cannot mount internal hugetlbfs for page size %uK",
> + ps_kb);
> + error = PTR_ERR(hugetlbfs_vfsmount[i]);
> + hugetlbfs_vfsmount[i] = NULL;
> + }
> + i++;
> }
hm, that's a bit messed up.
--- a/fs/hugetlbfs/inode.c~mm-support-more-pagesizes-for-map_hugetlb-shm_hugetlb-v7-fix
+++ a/fs/hugetlbfs/inode.c
@@ -1049,7 +1049,7 @@ static int __init init_hugetlbfs_fs(void
goto out;
i = 0;
- for_each_hstate (h) {
+ for_each_hstate(h) {
char buf[50];
unsigned ps_kb = 1U << (h->order + PAGE_SHIFT - 10);
@@ -1058,9 +1058,8 @@ static int __init init_hugetlbfs_fs(void
buf);
if (IS_ERR(hugetlbfs_vfsmount[i])) {
- pr_err(
- "hugetlb: Cannot mount internal hugetlbfs for page size %uK",
- ps_kb);
+ pr_err("hugetlb: Cannot mount internal hugetlbfs for "
+ "page size %uK", ps_kb);
error = PTR_ERR(hugetlbfs_vfsmount[i]);
hugetlbfs_vfsmount[i] = NULL;
}
@@ -1090,7 +1089,7 @@ static void __exit exit_hugetlbfs_fs(voi
rcu_barrier();
kmem_cache_destroy(hugetlbfs_inode_cachep);
i = 0;
- for_each_hstate (h)
+ for_each_hstate(h)
kern_unmount(hugetlbfs_vfsmount[i++]);
unregister_filesystem(&hugetlbfs_fs_type);
bdi_destroy(&hugetlbfs_backing_dev_info);
(we're not supposed to split strings like that, but screw 'em!)
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