[Qemu-devel] [PATCH 16/23] userfaultfd: allocate the userfaultfd_ctx cacheline aligned

[Andrea Arcangeli]

Use proper slab to guarantee alignment.

Signed-off-by: Andrea Arcangeli <address@hidden>
---
 fs/userfaultfd.c | 39 +++++++++++++++++++++++++++++++--------
 1 file changed, 31 insertions(+), 8 deletions(-)

diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index 3d26f41..5542fe7 100644
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -27,20 +27,26 @@
 #include <linux/ioctl.h>
 #include <linux/security.h>
 
+static struct kmem_cache *userfaultfd_ctx_cachep __read_mostly;
+
 enum userfaultfd_state {
        UFFD_STATE_WAIT_API,
        UFFD_STATE_RUNNING,
 };
 
+/*
+ * Start with fault_pending_wqh and fault_wqh so they're more likely
+ * to be in the same cacheline.
+ */
 struct userfaultfd_ctx {
-       /* pseudo fd refcounting */
-       atomic_t refcount;
        /* waitqueue head for the pending (i.e. not read) userfaults */
        wait_queue_head_t fault_pending_wqh;
        /* waitqueue head for the userfaults */
        wait_queue_head_t fault_wqh;
        /* waitqueue head for the pseudo fd to wakeup poll/read */
        wait_queue_head_t fd_wqh;
+       /* pseudo fd refcounting */
+       atomic_t refcount;
        /* userfaultfd syscall flags */
        unsigned int flags;
        /* state machine */
@@ -117,7 +123,7 @@ static void userfaultfd_ctx_put(struct userfaultfd_ctx *ctx)
                VM_BUG_ON(spin_is_locked(&ctx->fd_wqh.lock));
                VM_BUG_ON(waitqueue_active(&ctx->fd_wqh));
                mmput(ctx->mm);
-               kfree(ctx);
+               kmem_cache_free(userfaultfd_ctx_cachep, ctx);
        }
 }
 
@@ -987,6 +993,15 @@ static const struct file_operations userfaultfd_fops = {
        .llseek         = noop_llseek,
 };
 
+static void init_once_userfaultfd_ctx(void *mem)
+{
+       struct userfaultfd_ctx *ctx = (struct userfaultfd_ctx *) mem;
+
+       init_waitqueue_head(&ctx->fault_pending_wqh);
+       init_waitqueue_head(&ctx->fault_wqh);
+       init_waitqueue_head(&ctx->fd_wqh);
+}
+
 /**
  * userfaultfd_file_create - Creates an userfaultfd file pointer.
  * @flags: Flags for the userfaultfd file.
@@ -1017,14 +1032,11 @@ static struct file *userfaultfd_file_create(int flags)
                goto out;
 
        file = ERR_PTR(-ENOMEM);
-       ctx = kmalloc(sizeof(*ctx), GFP_KERNEL);
+       ctx = kmem_cache_alloc(userfaultfd_ctx_cachep, GFP_KERNEL);
        if (!ctx)
                goto out;
 
        atomic_set(&ctx->refcount, 1);
-       init_waitqueue_head(&ctx->fault_pending_wqh);
-       init_waitqueue_head(&ctx->fault_wqh);
-       init_waitqueue_head(&ctx->fd_wqh);
        ctx->flags = flags;
        ctx->state = UFFD_STATE_WAIT_API;
        ctx->released = false;
@@ -1035,7 +1047,7 @@ static struct file *userfaultfd_file_create(int flags)
        file = anon_inode_getfile("[userfaultfd]", &userfaultfd_fops, ctx,
                                  O_RDWR | (flags & UFFD_SHARED_FCNTL_FLAGS));
        if (IS_ERR(file))
-               kfree(ctx);
+               kmem_cache_free(userfaultfd_ctx_cachep, ctx);
 out:
        return file;
 }
@@ -1064,3 +1076,14 @@ err_put_unused_fd:
 
        return error;
 }
+
+static int __init userfaultfd_init(void)
+{
+       userfaultfd_ctx_cachep = kmem_cache_create("userfaultfd_ctx_cache",
+                                               sizeof(struct userfaultfd_ctx),
+                                               0,
+                                               SLAB_HWCACHE_ALIGN|SLAB_PANIC,
+                                               init_once_userfaultfd_ctx);
+       return 0;
+}
+__initcall(userfaultfd_init);