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authorBenjamin Marzinski <bmarzins@redhat.com>2015-12-01 17:46:55 +0300
committerBob Peterson <rpeterso@redhat.com>2015-12-14 21:19:37 +0300
commit471f3db2786bc32011d6693413eb93b0c3da2579 (patch)
treea3af645fd5dbb014bffa50a715422b954e83564f /fs/gfs2/dir.c
parent340174722929d80a107120400bab527cfc7e47f1 (diff)
downloadlinux-471f3db2786bc32011d6693413eb93b0c3da2579.tar.xz
gfs2: change gfs2 readdir cookie
gfs2 currently returns 31 bits of filename hash as a cookie that readdir uses for an offset into the directory. When there are a large number of directory entries, the likelihood of a collision goes up way too quickly. GFS2 will now return cookies that are guaranteed unique for a while, and then fail back to using 30 bits of filename hash. Specifically, the directory leaf blocks are divided up into chunks based on the minimum size of a gfs2 directory entry (48 bytes). Each entry's cookie is based off the chunk where it starts, in the linked list of leaf blocks that it hashes to (there are 131072 hash buckets). Directory entries will have unique names until they take reach chunk 8192. Assuming the largest filenames possible, and the least efficient spacing possible, this new method will still be able to return unique names when the previous method has statistically more than a 99% chance of a collision. The non-unique names it fails back to are guaranteed to not collide with the unique names. unique cookies will be in this format: - 1 bit "0" to make sure the the returned cookie is positive - 17 bits for the hash table index - 1 bit for the mode "0" - 13 bits for the offset non-unique cookies will be in this format: - 1 bit "0" to make sure the the returned cookie is positive - 17 bits for the hash table index - 1 bit for the mode "1" - 13 more bits of the name hash Another benefit of location based cookies, is that once a directory's exhash table is fully extended (so that multiple hash table indexs do not use the same leaf blocks), gfs2 can skip sorting the directory entries until it reaches the non-unique ones, and then it only needs to sort these. This provides a significant speed up for directory reads of very large directories. The only issue is that for these cookies to continue to point to the correct entry as files are added and removed from the directory, gfs2 must keep the entries at the same offset in the leaf block when they are split (see my previous patch). This means that until all the nodes in a cluster are running with code that will split the directory leaf blocks this way, none of the nodes can use the new cookie code. To deal with this, gfs2 now has the mount option loccookie, which, if set, will make it return these new location based cookies. This option must not be set until all nodes in the cluster are at least running this version of the kernel code, and you have guaranteed that there are no outstanding cookies required by other software, such as NFS. gfs2 uses some of the extra space at the end of the gfs2_dirent structure to store the calculated readdir cookies. This keeps us from needing to allocate a seperate array to hold these values. gfs2 recomputes the cookie stored in de_cookie for every readdir call. The time it takes to do so is small, and if gfs2 expected this value to be saved on disk, the new code wouldn't work correctly on filesystems created with an earlier version of gfs2. One issue with adding de_cookie to the union in the gfs2_dirent structure is that it caused the union to align itself to a 4 byte boundary, instead of its previous 2 byte boundary. This changed the offset of de_rahead. To solve that, I pulled de_rahead out of the union, since it does not need to be there. Signed-off-by: Benjamin Marzinski <bmarzins@redhat.com> Signed-off-by: Bob Peterson <rpeterso@redhat.com>
Diffstat (limited to 'fs/gfs2/dir.c')
-rw-r--r--fs/gfs2/dir.c91
1 files changed, 71 insertions, 20 deletions
diff --git a/fs/gfs2/dir.c b/fs/gfs2/dir.c
index 4ee008c6d64b..6a92592304fb 100644
--- a/fs/gfs2/dir.c
+++ b/fs/gfs2/dir.c
@@ -82,6 +82,8 @@
#define gfs2_disk_hash2offset(h) (((u64)(h)) >> 1)
#define gfs2_dir_offset2hash(p) ((u32)(((u64)(p)) << 1))
+#define GFS2_HASH_INDEX_MASK 0xffffc000
+#define GFS2_USE_HASH_FLAG 0x2000
struct qstr gfs2_qdot __read_mostly;
struct qstr gfs2_qdotdot __read_mostly;
@@ -1223,10 +1225,10 @@ static int compare_dents(const void *a, const void *b)
int ret = 0;
dent_a = *(const struct gfs2_dirent **)a;
- hash_a = be32_to_cpu(dent_a->de_hash);
+ hash_a = dent_a->de_cookie;
dent_b = *(const struct gfs2_dirent **)b;
- hash_b = be32_to_cpu(dent_b->de_hash);
+ hash_b = dent_b->de_cookie;
if (hash_a > hash_b)
ret = 1;
@@ -1264,19 +1266,20 @@ static int compare_dents(const void *a, const void *b)
*/
static int do_filldir_main(struct gfs2_inode *dip, struct dir_context *ctx,
- const struct gfs2_dirent **darr, u32 entries,
- int *copied)
+ struct gfs2_dirent **darr, u32 entries,
+ u32 sort_start, int *copied)
{
const struct gfs2_dirent *dent, *dent_next;
u64 off, off_next;
unsigned int x, y;
int run = 0;
- sort(darr, entries, sizeof(struct gfs2_dirent *), compare_dents, NULL);
+ if (sort_start < entries)
+ sort(&darr[sort_start], entries - sort_start,
+ sizeof(struct gfs2_dirent *), compare_dents, NULL);
dent_next = darr[0];
- off_next = be32_to_cpu(dent_next->de_hash);
- off_next = gfs2_disk_hash2offset(off_next);
+ off_next = dent_next->de_cookie;
for (x = 0, y = 1; x < entries; x++, y++) {
dent = dent_next;
@@ -1284,8 +1287,7 @@ static int do_filldir_main(struct gfs2_inode *dip, struct dir_context *ctx,
if (y < entries) {
dent_next = darr[y];
- off_next = be32_to_cpu(dent_next->de_hash);
- off_next = gfs2_disk_hash2offset(off_next);
+ off_next = dent_next->de_cookie;
if (off < ctx->pos)
continue;
@@ -1332,6 +1334,40 @@ static void *gfs2_alloc_sort_buffer(unsigned size)
return ptr;
}
+
+static int gfs2_set_cookies(struct gfs2_sbd *sdp, struct buffer_head *bh,
+ unsigned leaf_nr, struct gfs2_dirent **darr,
+ unsigned entries)
+{
+ int sort_id = -1;
+ int i;
+
+ for (i = 0; i < entries; i++) {
+ unsigned offset;
+
+ darr[i]->de_cookie = be32_to_cpu(darr[i]->de_hash);
+ darr[i]->de_cookie = gfs2_disk_hash2offset(darr[i]->de_cookie);
+
+ if (!sdp->sd_args.ar_loccookie)
+ continue;
+ offset = (char *)(darr[i]) -
+ (bh->b_data + gfs2_dirent_offset(bh->b_data));
+ offset /= GFS2_MIN_DIRENT_SIZE;
+ offset += leaf_nr * sdp->sd_max_dents_per_leaf;
+ if (offset >= GFS2_USE_HASH_FLAG ||
+ leaf_nr >= GFS2_USE_HASH_FLAG) {
+ darr[i]->de_cookie |= GFS2_USE_HASH_FLAG;
+ if (sort_id < 0)
+ sort_id = i;
+ continue;
+ }
+ darr[i]->de_cookie &= GFS2_HASH_INDEX_MASK;
+ darr[i]->de_cookie |= offset;
+ }
+ return sort_id;
+}
+
+
static int gfs2_dir_read_leaf(struct inode *inode, struct dir_context *ctx,
int *copied, unsigned *depth,
u64 leaf_no)
@@ -1341,12 +1377,11 @@ static int gfs2_dir_read_leaf(struct inode *inode, struct dir_context *ctx,
struct buffer_head *bh;
struct gfs2_leaf *lf;
unsigned entries = 0, entries2 = 0;
- unsigned leaves = 0;
- const struct gfs2_dirent **darr, *dent;
+ unsigned leaves = 0, leaf = 0, offset, sort_offset;
+ struct gfs2_dirent **darr, *dent;
struct dirent_gather g;
struct buffer_head **larr;
- int leaf = 0;
- int error, i;
+ int error, i, need_sort = 0, sort_id;
u64 lfn = leaf_no;
do {
@@ -1362,6 +1397,11 @@ static int gfs2_dir_read_leaf(struct inode *inode, struct dir_context *ctx,
brelse(bh);
} while(lfn);
+ if (*depth < GFS2_DIR_MAX_DEPTH || !sdp->sd_args.ar_loccookie) {
+ need_sort = 1;
+ sort_offset = 0;
+ }
+
if (!entries)
return 0;
@@ -1375,8 +1415,8 @@ static int gfs2_dir_read_leaf(struct inode *inode, struct dir_context *ctx,
larr = gfs2_alloc_sort_buffer((leaves + entries + 99) * sizeof(void *));
if (!larr)
goto out;
- darr = (const struct gfs2_dirent **)(larr + leaves);
- g.pdent = darr;
+ darr = (struct gfs2_dirent **)(larr + leaves);
+ g.pdent = (const struct gfs2_dirent **)darr;
g.offset = 0;
lfn = leaf_no;
@@ -1387,6 +1427,7 @@ static int gfs2_dir_read_leaf(struct inode *inode, struct dir_context *ctx,
lf = (struct gfs2_leaf *)bh->b_data;
lfn = be64_to_cpu(lf->lf_next);
if (lf->lf_entries) {
+ offset = g.offset;
entries2 += be16_to_cpu(lf->lf_entries);
dent = gfs2_dirent_scan(inode, bh->b_data, bh->b_size,
gfs2_dirent_gather, NULL, &g);
@@ -1404,17 +1445,26 @@ static int gfs2_dir_read_leaf(struct inode *inode, struct dir_context *ctx,
goto out_free;
}
error = 0;
+ sort_id = gfs2_set_cookies(sdp, bh, leaf, &darr[offset],
+ be16_to_cpu(lf->lf_entries));
+ if (!need_sort && sort_id >= 0) {
+ need_sort = 1;
+ sort_offset = offset + sort_id;
+ }
larr[leaf++] = bh;
} else {
+ larr[leaf++] = NULL;
brelse(bh);
}
} while(lfn);
BUG_ON(entries2 != entries);
- error = do_filldir_main(ip, ctx, darr, entries, copied);
+ error = do_filldir_main(ip, ctx, darr, entries, need_sort ?
+ sort_offset : entries, copied);
out_free:
for(i = 0; i < leaf; i++)
- brelse(larr[i]);
+ if (larr[i])
+ brelse(larr[i]);
kvfree(larr);
out:
return error;
@@ -1520,7 +1570,7 @@ int gfs2_dir_read(struct inode *inode, struct dir_context *ctx,
struct gfs2_inode *dip = GFS2_I(inode);
struct gfs2_sbd *sdp = GFS2_SB(inode);
struct dirent_gather g;
- const struct gfs2_dirent **darr, *dent;
+ struct gfs2_dirent **darr, *dent;
struct buffer_head *dibh;
int copied = 0;
int error;
@@ -1544,7 +1594,7 @@ int gfs2_dir_read(struct inode *inode, struct dir_context *ctx,
/* 96 is max number of dirents which can be stuffed into an inode */
darr = kmalloc(96 * sizeof(struct gfs2_dirent *), GFP_NOFS);
if (darr) {
- g.pdent = darr;
+ g.pdent = (const struct gfs2_dirent **)darr;
g.offset = 0;
dent = gfs2_dirent_scan(inode, dibh->b_data, dibh->b_size,
gfs2_dirent_gather, NULL, &g);
@@ -1561,8 +1611,9 @@ int gfs2_dir_read(struct inode *inode, struct dir_context *ctx,
error = -EIO;
goto out;
}
+ gfs2_set_cookies(sdp, dibh, 0, darr, dip->i_entries);
error = do_filldir_main(dip, ctx, darr,
- dip->i_entries, &copied);
+ dip->i_entries, 0, &copied);
out:
kfree(darr);
}