exfat: optimize allocation bitmap loading time

Loading the allocation bitmap is very slow if user set the small cluster
size on large partition.

For optimizing it, This patch uses sb_breadahead() read the allocation
bitmap. It will improve the mount time.

The following is the result of about 4TB partition(2KB cluster size)
on my target.

without patch:
real 0m41.746s
user 0m0.011s
sys 0m0.000s

with patch:
real 0m2.525s
user 0m0.008s
sys 0m0.008s

Reviewed-by: Sungjong Seo <sj1557.seo@samsung.com>
Reviewed-by: Yuezhang Mo <Yuezhang.Mo@sony.com>
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>

diff --git a/fs/exfat/balloc.c b/fs/exfat/balloc.c
index 071448adbd5d974c23b75085587f9d0cece3fb99..2d2d510f2372cbccbf45574a8fc9b6bb30e4713d 100644 (file)
--- a/fs/exfat/balloc.c
+++ b/fs/exfat/balloc.c
@@ -7,6 +7,7 @@
 #include <linux/slab.h>
 #include <linux/bitmap.h>
 #include <linux/buffer_head.h>
+#include <linux/backing-dev.h>
 
 #include "exfat_raw.h"
 #include "exfat_fs.h"
@@ -73,9 +74,11 @@ static int exfat_allocate_bitmap(struct super_block *sb,
                struct exfat_dentry *ep)
 {
        struct exfat_sb_info *sbi = EXFAT_SB(sb);
+       struct blk_plug plug;
        long long map_size;
        unsigned int i, j, need_map_size;
        sector_t sector;
+       unsigned int max_ra_count;
 
        sbi->map_clu = le32_to_cpu(ep->dentry.bitmap.start_clu);
        map_size = le64_to_cpu(ep->dentry.bitmap.size);
@@ -99,7 +102,17 @@ static int exfat_allocate_bitmap(struct super_block *sb,
                return -ENOMEM;
 
        sector = exfat_cluster_to_sector(sbi, sbi->map_clu);
+       max_ra_count = min(sb->s_bdi->ra_pages, sb->s_bdi->io_pages) <<
+               (PAGE_SHIFT - sb->s_blocksize_bits);
        for (i = 0; i < sbi->map_sectors; i++) {
+               /* Trigger the next readahead in advance. */
+               if (0 == (i % max_ra_count)) {
+                       blk_start_plug(&plug);
+                       for (j = i; j < min(max_ra_count, sbi->map_sectors - i) + i; j++)
+                               sb_breadahead(sb, sector + j);
+                       blk_finish_plug(&plug);
+               }
+
                sbi->vol_amap[i] = sb_bread(sb, sector + i);
                if (!sbi->vol_amap[i])
                        goto err_out;