diff options
| author | Justus Winter <4winter@informatik.uni-hamburg.de> | 2014-04-24 17:44:14 +0200 |
|---|---|---|
| committer | Justus Winter <4winter@informatik.uni-hamburg.de> | 2014-05-13 16:45:51 +0200 |
| commit | 134b450cb65b1986c78e0b292cff78c2f1882a2b (patch) | |
| tree | 331c2a170decbe42ae34b0df2bc609942744ab6b /ext2fs/ext2fs.h | |
| parent | 261d957ebe4cf16aed76eed24b5bfd32f1f5a79a (diff) | |
ext2fs: cache the superblock
Previously, the superblock was mmaped and a pointer stored in sblock
by map_hypermetadata. This memory is backed by our disk pager.
This is rather unfortunate, as this means that whenever we read a
value from that location, we might generate a request our disk pager.
This amplifies the so-called thread-storm problem.
Rather than relying on a mmaped region of memory, just use the data
loaded by get_hypermetadata.
* ext2fs/hyper.c (get_hypermetadata): Do not free sblock.
(mapped_sblock): New variable.
(map_hypermetadata): Map the superblock to mapped_sblock instead.
(diskfs_set_hypermetadata): Copy superblock into mapped_superblock.
* ext2fs/ext2fs.h (get_hypermetadata, map_hypermetadata): Adjust
comments accordingly.
Diffstat (limited to 'ext2fs/ext2fs.h')
| -rw-r--r-- | ext2fs/ext2fs.h | 8 |
1 files changed, 6 insertions, 2 deletions
diff --git a/ext2fs/ext2fs.h b/ext2fs/ext2fs.h index e01d1a59..3422af2f 100644 --- a/ext2fs/ext2fs.h +++ b/ext2fs/ext2fs.h @@ -297,10 +297,14 @@ unsigned log2_stat_blocks_per_fs_block; /* A handy page of page-aligned zeros. */ vm_address_t zeroblock; -/* Get the superblock from the disk, & setup various global info from it. */ +/* Get the superblock from the disk, point `sblock' to it, and setup + various global info from it. */ void get_hypermetadata (); -/* Map `sblock' and `group_desc_image' pointers to disk cache. */ +/* Map `group_desc_image' pointers to disk cache. Also, establish a + non-exported mapping to the superblock that will be used by + diskfs_set_hypermetadata to update the superblock from the cache + `sblock' points to. */ void map_hypermetadata (); /* ---------------------------------------------------------------- */ |