btrfs: send: lower memory requirements in common case

The fs_path structure uses an inline buffer and falls back to a chain of
allocations, but vmalloc is not necessary because PATH_MAX fits into
PAGE_SIZE.

The size of fs_path has been reduced to 256 bytes from PAGE_SIZE,
usually 4k. Experimental measurements show that most paths on a single
filesystem do not exceed 200 bytes, and these get stored into the inline
buffer directly, which is now 230 bytes. Longer paths are kmalloced when
needed.

Signed-off-by: David Sterba <dsterba@suse.cz>
Signed-off-by: Josef Bacik <jbacik@fb.com>

diff --git a/fs/btrfs/send.c b/fs/btrfs/send.c
index a2621e7..a5da82f 100644 (file)
--- a/fs/btrfs/send.c
+++ b/fs/btrfs/send.c
@@ -57,7 +57,12 @@ struct fs_path {
                        unsigned short reversed:1;
                        char inline_buf[];
                };
-               char pad[PAGE_SIZE];
+               /*
+                * Average path length does not exceed 200 bytes, we'll have
+                * better packing in the slab and higher chance to satisfy
+                * a allocation later during send.
+                */
+               char pad[256];
        };
 };
 #define FS_PATH_INLINE_SIZE \
@@ -262,12 +267,8 @@ static void fs_path_free(struct fs_path *p)
 {
        if (!p)
                return;
-       if (p->buf != p->inline_buf) {
-               if (is_vmalloc_addr(p->buf))
-                       vfree(p->buf);
-               else
-                       kfree(p->buf);
-       }
+       if (p->buf != p->inline_buf)
+               kfree(p->buf);
        kfree(p);
 }
 
@@ -287,40 +288,31 @@ static int fs_path_ensure_buf(struct fs_path *p, int len)
        if (p->buf_len >= len)
                return 0;
 
-       path_len = p->end - p->start;
-       old_buf_len = p->buf_len;
-       len = PAGE_ALIGN(len);
-
+       /*
+        * First time the inline_buf does not suffice
+        */
        if (p->buf == p->inline_buf) {
-               tmp_buf = kmalloc(len, GFP_NOFS | __GFP_NOWARN);
-               if (!tmp_buf) {
-                       tmp_buf = vmalloc(len);
-                       if (!tmp_buf)
-                               return -ENOMEM;
-               }
-               memcpy(tmp_buf, p->buf, p->buf_len);
-               p->buf = tmp_buf;
-               p->buf_len = len;
+               p->buf = kmalloc(len, GFP_NOFS);
+               if (!p->buf)
+                       return -ENOMEM;
+               /*
+                * The real size of the buffer is bigger, this will let the
+                * fast path happen most of the time
+                */
+               p->buf_len = ksize(p->buf);
        } else {
-               if (is_vmalloc_addr(p->buf)) {
-                       tmp_buf = vmalloc(len);
-                       if (!tmp_buf)
-                               return -ENOMEM;
-                       memcpy(tmp_buf, p->buf, p->buf_len);
-                       vfree(p->buf);
-               } else {
-                       tmp_buf = krealloc(p->buf, len, GFP_NOFS);
-                       if (!tmp_buf) {
-                               tmp_buf = vmalloc(len);
-                               if (!tmp_buf)
-                                       return -ENOMEM;
-                               memcpy(tmp_buf, p->buf, p->buf_len);
-                               kfree(p->buf);
-                       }
-               }
-               p->buf = tmp_buf;
-               p->buf_len = len;
+               char *tmp;
+
+               tmp = krealloc(p->buf, len, GFP_NOFS);
+               if (!tmp)
+                       return -ENOMEM;
+               p->buf = tmp;
+               p->buf_len = ksize(p->buf);
        }
+
+       path_len = p->end - p->start;
+       old_buf_len = p->buf_len;
+
        if (p->reversed) {
                tmp_buf = p->buf + old_buf_len - path_len - 1;
                p->end = p->buf + p->buf_len - 1;
@@ -911,9 +903,7 @@ static int iterate_dir_item(struct btrfs_root *root, struct btrfs_path *path,
        struct btrfs_dir_item *di;
        struct btrfs_key di_key;
        char *buf = NULL;
-       char *buf2 = NULL;
-       int buf_len;
-       int buf_virtual = 0;
+       const int buf_len = PATH_MAX;
        u32 name_len;
        u32 data_len;
        u32 cur;
@@ -923,7 +913,6 @@ static int iterate_dir_item(struct btrfs_root *root, struct btrfs_path *path,
        int num;
        u8 type;
 
-       buf_len = PAGE_SIZE;
        buf = kmalloc(buf_len, GFP_NOFS);
        if (!buf) {
                ret = -ENOMEM;
@@ -945,30 +934,12 @@ static int iterate_dir_item(struct btrfs_root *root, struct btrfs_path *path,
                type = btrfs_dir_type(eb, di);
                btrfs_dir_item_key_to_cpu(eb, di, &di_key);
 
+               /*
+                * Path too long
+                */
                if (name_len + data_len > buf_len) {
-                       buf_len = PAGE_ALIGN(name_len + data_len);
-                       if (buf_virtual) {
-                               buf2 = vmalloc(buf_len);
-                               if (!buf2) {
-                                       ret = -ENOMEM;
-                                       goto out;
-                               }
-                               vfree(buf);
-                       } else {
-                               buf2 = krealloc(buf, buf_len, GFP_NOFS);
-                               if (!buf2) {
-                                       buf2 = vmalloc(buf_len);
-                                       if (!buf2) {
-                                               ret = -ENOMEM;
-                                               goto out;
-                                       }
-                                       kfree(buf);
-                                       buf_virtual = 1;
-                               }
-                       }
-
-                       buf = buf2;
-                       buf2 = NULL;
+                       ret = -ENAMETOOLONG;
+                       goto out;
                }
 
                read_extent_buffer(eb, buf, (unsigned long)(di + 1),
@@ -991,10 +962,7 @@ static int iterate_dir_item(struct btrfs_root *root, struct btrfs_path *path,
        }
 
 out:
-       if (buf_virtual)
-               vfree(buf);
-       else
-               kfree(buf);
+       kfree(buf);
        return ret;
 }