David Sterba
2014-Feb-05 15:17 UTC
[PATCH v2] 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>
---
v2:
- intel build test reports that krealloc should not reuse the buffer for return
value, though it's not a problem in our case, a failed allocation leads to
immediate return, let's use a temporary variable to keep the check happy
fs/btrfs/send.c | 106 +++++++++++++++++++-----------------------------------
1 files changed, 37 insertions(+), 69 deletions(-)
diff --git a/fs/btrfs/send.c b/fs/btrfs/send.c
index 1f09c74e1c1f..dd0b02adb1e6 100644
--- 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;
}
--
1.7.9
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