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SubjectRe: [PATCH][FAT] FAT dirent scan with hin take #3


OGAWA Hirofumi wrote:
:
>
>
> The fat_lookup_hint is one per task. And fat_lookup_hint is tracking
> the task's access. If access is sequential, it returns the hint, and
> if not, it returns 0. I made the dirty patch just for explaining what
> I said.

Sorry late, at the last weekend I looked into the patch you post and run it.
I got your idea, now. I would propose following changes on it and attached
modified patch into this mail.

1. The original patch has system wide 16 entries access-tracking buffer.
I modified system has one access-tracking buffer for each mounted FS instance.
And it allocates the buffer on mounting as a part of FS dependent super block.

2. On looking up hints, the original patch try to find the entry which has
same pid and dir. If matched entry is not found, it uses always zero.
However we can expect locality beyond process, so I changes a little bit,
behavior of fail to find the matched entry.

try to find the entry which has same pid and dir.
if matched entry is not found, try to find recent access to same dir.

3. With the original code, the access-tracking buffer can hold just one entry
for one pid. I think it is better to have few entries for one pid.
I modified patch to have up to 3 entires (less than 1/4 of total entries) for
each pid.

4. Originally window size to determine locality seems wide due to using max len
of LFN(MSDOS_SLOTS), like;
WIN_BOTTOM = 5 * MSDOS_SLOTS * size of entry
We can use the value based on statistic instead of MSDOS_SLOTS. I checked with
my FC3 installed system, most files(over 99%) have less than or equal to 48
chars file name length. So use 9 instead of 21(MSDOS_SLOTS)

5. Adding short name entry support.

And I have fixed a bug which makes infinite loop on lookup empty dir
after all files were removed.

> However, these lookup-hint approaches seems the hack after all....
> Hhmmm...

I have another idea as following;

On reading blocks ahead, try to build dentry caches for all FAT dir entries
which reside in those blocks. And start dir-scan at some position
close to bottom of the latest read-ahead block, instead of zero.

However, I guess this tends to consume dentry caches and it may have affects
on other area.

As you said, I think "lookup-hint" is hack, but not so bad. Because it has
no side effect to other area and memory consumption is predictable.

--
Hiroyuki Machida
Signed-off-by: Hiroyuki Machida <machida@sm.sony.co.jp>
Signed-off-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
---
fs/fat/dir.c | 232 ++++++++++++++++++++++++++++++++++++++++++++---
fs/fat/inode.c | 7 +
include/linux/msdos_fs.h | 19 +++


3 files changed, 246 insertions(+), 12 deletions(-)
diff -r -up linux-2.6.13/fs/fat/dir.c linux-2.6.13-scan2/fs/fat/dir.c
--- linux-2.6.13/fs/fat/dir.c 2005-08-29 08:41:01.000000000 +0900
+++ linux-2.6.13-scan2/fs/fat/dir.c 2005-09-14 17:20:38.220767449 +0900
@@ -22,6 +22,185 @@
#include <linux/buffer_head.h>
#include <asm/uaccess.h>

+void fat_lkup_hint_init_sb(struct super_block *sb)
+{
+ struct msdos_sb_info *sbi = MSDOS_SB(sb);
+
+ sbi->lkup_hint_lock = SPIN_LOCK_UNLOCKED;
+ INIT_LIST_HEAD(&sbi->lkup_hint_head);
+ sbi->lkup_hint_freemap = 0;
+ sbi->lkup_hint_freemap = ~sbi->lkup_hint_freemap;
+}
+
+void fat_lkup_hint_inval(struct inode *dir)
+{
+ struct super_block *sb = dir->i_sb;
+ struct msdos_sb_info *sbi = MSDOS_SB(sb);
+ struct fat_lookup_hint *hint, *n;
+ int i;
+
+ spin_lock(&sbi->lkup_hint_lock);
+ list_for_each_entry_safe(hint, n, &sbi->lkup_hint_head, lru_list) {
+ if (hint->dir == dir) {
+ list_del_init(&hint->lru_list);
+ i = hint - &(sbi->lkup_hint[0]);
+ sbi->lkup_hint_freemap |= (1 << i);
+ }
+ }
+ spin_unlock(&sbi->lkup_hint_lock);
+}
+
+/*
+ * AVG_MSDOS_SLOTS is selected so that it can store 48 chars file name length.
+ *
+ * According raugh observation, most files in Linux installed system have
+ * less than or equal to 48 chars file name length.
+ *
+ * Following is one of statistic information;
+ *
+ * total # of files(*1) 9193
+ * max length of file name 52 chars
+ *
+ * # of files over 48 chars name length 36
+ * % covered by 48 chars name length 99.6%
+ *
+ * # of files over 32 chars name length 517
+ * % covered by 32 chars name length 94.3%
+ *
+ * *1) # of file, dir and symlink which has over 2 chars
+ * file name length.
+ *
+ */
+#define AVG_MSDOS_SLOTS (8+1)
+#define WIN_LFN_TOP (3 * AVG_MSDOS_SLOTS * sizeof(struct msdos_dir_entry))
+#define WIN_LFN_BOTTOM (5 * AVG_MSDOS_SLOTS * sizeof(struct msdos_dir_entry))
+
+#define WIN_TOP (3 * sizeof(struct msdos_dir_entry))
+#define WIN_BOTTOM (5 * sizeof(struct msdos_dir_entry))
+
+static inline
+loff_t get_syswide_hint(loff_t pos, struct fat_lookup_hint *hint)
+{
+ /*
+ * NOTE: If you don't expect locality beyond process,
+ * make this return 0 always, instead of following.
+ */
+ return (pos == 0) ? hint->last_pos : pos;
+}
+
+static loff_t fat_lkup_hint_get(struct inode *dir, int is_lfn)
+{
+ struct super_block *sb = dir->i_sb;
+ struct fat_lookup_hint *hint;
+ struct msdos_sb_info *sbi = MSDOS_SB(sb);
+ loff_t win_top;
+ unsigned int rnd_flg;
+ loff_t pos = 0;
+
+ if (is_lfn) {
+ rnd_flg = FAT_LKUP_ST_LFN_RANDOM;
+ win_top = WIN_LFN_TOP;
+ } else {
+ rnd_flg = FAT_LKUP_ST_RANDOM;
+ win_top = WIN_TOP;
+ }
+
+ spin_lock(&sbi->lkup_hint_lock);
+ list_for_each_entry(hint, &sbi->lkup_hint_head, lru_list) {
+ if (hint->dir == dir) {
+ if (!(hint->state & rnd_flg)) {
+ if (hint->pid == current->pid) {
+ pos = hint->last_pos;
+ break;
+ }
+ /* expect locality beyond process */
+ pos = get_syswide_hint(pos, hint);
+ }
+ }
+ }
+ spin_unlock(&sbi->lkup_hint_lock);
+ return max(0LL, pos - win_top);
+}
+
+/*
+ * NOTE: If you don't want multiple entries for
+ * same pid, set this to 1.
+ */
+#define LKUP_MULTIENT_MAX (FAT_LKUP_HINT_MAX/4-1)
+
+
+/* caller must hold dir->i_sem */
+static void fat_lkup_hint_add(struct inode *dir, loff_t pos)
+{
+ struct super_block *sb = dir->i_sb;
+ struct fat_lookup_hint *p, *hint = NULL;
+ loff_t win_start, win_end;
+ struct msdos_sb_info *sbi = MSDOS_SB(sb);
+ int nr_pid_match = 0;
+ unsigned int state;
+
+ spin_lock(&sbi->lkup_hint_lock);
+ /* find out same pid entry */
+ list_for_each_entry(p, &sbi->lkup_hint_head, lru_list) {
+ if (p->pid == current->pid) {
+ nr_pid_match ++;
+ if (p->dir == dir) {
+ hint = p;
+ goto match;
+ }
+ if (!hint)
+ hint = p;
+ }
+ }
+
+ if (nr_pid_match < LKUP_MULTIENT_MAX)
+ hint = NULL;
+
+ if (hint == NULL) {
+ int free_hint;
+ free_hint = ffs(sbi->lkup_hint_freemap);
+ if (free_hint) {
+ /* add the new entry */
+ free_hint --;
+ sbi->lkup_hint_freemap &= ~ (1<<(free_hint));
+ hint = &sbi->lkup_hint[free_hint];
+ INIT_LIST_HEAD(&hint->lru_list);
+ /* don't need to recheck hint */
+ } else {
+ /* replace the last entry */
+ struct list_head *p = sbi->lkup_hint_head.prev;
+ hint = list_entry(p, struct fat_lookup_hint, lru_list);
+ }
+ hint->pid = current->pid;
+ hint->dir = dir;
+ hint->last_pos = 0;
+ }
+
+match:
+ state = (FAT_LKUP_ST_RANDOM | FAT_LKUP_ST_LFN_RANDOM);
+ hint->last_pos = pos;
+ if (hint->dir != dir) {
+ hint->dir = dir;
+ } else {
+ win_start = hint->last_pos - WIN_TOP;
+ win_end = hint->last_pos + WIN_BOTTOM;
+ if (win_start <= pos && pos <= win_end) {
+ state &= ~FAT_LKUP_ST_RANDOM;
+ }
+ win_start = hint->last_pos - WIN_LFN_TOP;
+ win_end = hint->last_pos + WIN_LFN_BOTTOM;
+ if (win_start <= pos && pos <= win_end) {
+ state &= ~FAT_LKUP_ST_LFN_RANDOM;
+ }
+ }
+ hint->state = state;
+
+ /* update LRU list */
+ list_del(&hint->lru_list);
+ list_add(&hint->lru_list, &sbi->lkup_hint_head); /* put hint to head */
+ spin_unlock(&sbi->lkup_hint_lock);
+}
+
static inline loff_t fat_make_i_pos(struct super_block *sb,
struct buffer_head *bh,
struct msdos_dir_entry *de)
@@ -218,13 +397,23 @@ int fat_search_long(struct inode *inode,
int utf8 = sbi->options.utf8;
int anycase = (sbi->options.name_check != 's');
unsigned short opt_shortname = sbi->options.shortname;
- loff_t cpos = 0;
int chl, i, j, last_u, err;
+ loff_t cpos, start_off;
+ int reach_bottom = 0;

+ start_off = cpos = fat_lkup_hint_get(inode, 1);
err = -ENOENT;
while(1) {
- if (fat_get_entry(inode, &cpos, &bh, &de) == -1)
+top:
+ if (reach_bottom && cpos >= start_off)
goto EODir;
+ if (fat_get_entry(inode, &cpos, &bh, &de) == -1) {
+ if (!start_off || reach_bottom)
+ goto EODir;
+ reach_bottom++;
+ cpos = 0;
+ continue;
+ }
parse_record:
nr_slots = 0;
if (de->name[0] == DELETED_FLAG)
@@ -274,8 +463,13 @@ parse_long:
if (ds->id & 0x40) {
unicode[offset + 13] = 0;
}
- if (fat_get_entry(inode, &cpos, &bh, &de) < 0)
- goto EODir;
+ if (fat_get_entry(inode, &cpos, &bh, &de) < 0) {
+ if (!start_off || reach_bottom)
+ goto EODir;
+ reach_bottom++;
+ cpos = 0;
+ goto top;
+ }
if (slot == 0)
break;
ds = (struct msdos_dir_slot *) de;
@@ -363,6 +557,7 @@ Found:
sinfo->de = de;
sinfo->bh = bh;
sinfo->i_pos = fat_make_i_pos(sb, sinfo->bh, sinfo->de);
+ fat_lkup_hint_add(inode, sinfo->slot_off);
err = 0;
EODir:
if (unicode)
@@ -838,16 +1033,29 @@ int fat_scan(struct inode *dir, const un
struct fat_slot_info *sinfo)
{
struct super_block *sb = dir->i_sb;
+ int reach_bottom = 0;
+ loff_t start_off;

- sinfo->slot_off = 0;
+ start_off = sinfo->slot_off = fat_lkup_hint_get(dir, 0);
sinfo->bh = NULL;
- while (fat_get_short_entry(dir, &sinfo->slot_off, &sinfo->bh,
- &sinfo->de) >= 0) {
- if (!strncmp(sinfo->de->name, name, MSDOS_NAME)) {
- sinfo->slot_off -= sizeof(*sinfo->de);
- sinfo->nr_slots = 1;
- sinfo->i_pos = fat_make_i_pos(sb, sinfo->bh, sinfo->de);
- return 0;
+ while (1) {
+ if (fat_get_short_entry(dir, &sinfo->slot_off, &sinfo->bh,
+ &sinfo->de) >= 0) {
+ if (!strncmp(sinfo->de->name, name, MSDOS_NAME)) {
+ sinfo->slot_off -= sizeof(*sinfo->de);
+ sinfo->nr_slots = 1;
+ sinfo->i_pos = fat_make_i_pos(sb, sinfo->bh,
+ sinfo->de);
+ fat_lkup_hint_add(dir, sinfo->slot_off);
+ return 0;
+ }
+ if (reach_bottom && (start_off <= sinfo->slot_off))
+ break;
+ } else {
+ if (!start_off || reach_bottom)
+ break;
+ reach_bottom ++;
+ sinfo->slot_off = 0;
}
}
return -ENOENT;
diff -r -up linux-2.6.13/fs/fat/inode.c linux-2.6.13-scan2/fs/fat/inode.c
--- linux-2.6.13/fs/fat/inode.c 2005-08-29 08:41:01.000000000 +0900
+++ linux-2.6.13-scan2/fs/fat/inode.c 2005-09-14 17:24:21.446091170 +0900
@@ -342,6 +342,8 @@ static void fat_delete_inode(struct inod
clear_inode(inode);
}

+extern void fat_lkup_hint_inval(struct inode*);
+
static void fat_clear_inode(struct inode *inode)
{
struct msdos_sb_info *sbi = MSDOS_SB(inode->i_sb);
@@ -349,6 +351,7 @@ static void fat_clear_inode(struct inode
if (is_bad_inode(inode))
return;
lock_kernel();
+ fat_lkup_hint_inval(inode);
spin_lock(&sbi->inode_hash_lock);
fat_cache_inval_inode(inode);
hlist_del_init(&MSDOS_I(inode)->i_fat_hash);
@@ -1042,6 +1045,8 @@ static int fat_read_root(struct inode *i
return 0;
}

+extern void fat_lkup_hint_init_sb(struct super_block *sb);
+
/*
* Read the super block of an MS-DOS FS.
*/
@@ -1302,6 +1307,8 @@ int fat_fill_super(struct super_block *s
goto out_fail;
}

+ fat_lkup_hint_init_sb(sb);
+
return 0;

out_invalid:
diff -r -up linux-2.6.13/include/linux/msdos_fs.h linux-2.6.13-scan2/include/linux/msdos_fs.h
--- linux-2.6.13/include/linux/msdos_fs.h 2005-08-29 08:41:01.000000000 +0900
+++ linux-2.6.13-scan2/include/linux/msdos_fs.h 2005-09-14 17:22:38.223629408 +0900
@@ -185,6 +185,19 @@ struct fat_slot_info {
#include <linux/nls.h>
#include <linux/fs.h>

+#define FAT_LKUP_HINT_MAX 16
+/* assume FAT_LKUP_HINT_MAX <= sizeof(long)*8 */
+
+struct fat_lookup_hint {
+ struct list_head lru_list;
+ pid_t pid;
+ struct inode *dir;
+ loff_t last_pos;
+#define FAT_LKUP_ST_RANDOM 1
+#define FAT_LKUP_ST_LFN_RANDOM 2
+ unsigned int state;
+};
+
struct fat_mount_options {
uid_t fs_uid;
gid_t fs_gid;
@@ -241,6 +254,12 @@ struct msdos_sb_info {

spinlock_t inode_hash_lock;
struct hlist_head inode_hashtable[FAT_HASH_SIZE];
+
+ /* dirent lookup hints */
+ spinlock_t lkup_hint_lock;
+ struct list_head lkup_hint_head;
+ struct fat_lookup_hint lkup_hint[FAT_LKUP_HINT_MAX];
+ unsigned lkup_hint_freemap:FAT_LKUP_HINT_MAX;
};

#define FAT_CACHE_VALID 0 /* special case for valid cache */
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