Justus Winter, le Mon 12 May 2014 12:05:39 +0200, a écrit :
> 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.
Please also fix the comment in the declaration of map_hypermetadata in
ext2fs.h, then Ack.
> * 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/hyper.c | 19 +++++++++++--------
> 1 file changed, 11 insertions(+), 8 deletions(-)
>
> diff --git a/ext2fs/hyper.c b/ext2fs/hyper.c
> index 5bcc2ab..5f288bf 100644
> --- a/ext2fs/hyper.c
> +++ b/ext2fs/hyper.c
> @@ -61,7 +61,9 @@ get_hypermetadata (void)
> error_t err;
> size_t read = 0;
>
> - assert (! sblock);
> + if (sblock != NULL)
> + munmap (sblock, SBLOCK_SIZE);
> +
> err = store_read (store, SBLOCK_OFFS >> store->log2_block_size,
> SBLOCK_SIZE, (void **)&sblock, &read);
> if (err || read != SBLOCK_SIZE)
> @@ -161,19 +163,19 @@ get_hypermetadata (void)
> zeroblock = (vm_address_t) mmap (0, block_size, PROT_READ, MAP_ANON,
> 0, 0);
> assert (zeroblock != (vm_address_t) MAP_FAILED);
> }
> -
> - munmap (sblock, SBLOCK_SIZE);
> - sblock = NULL;
> }
>
> +static struct ext2_super_block *mapped_sblock;
> +
> void
> map_hypermetadata (void)
> {
> - sblock = (struct ext2_super_block *) boffs_ptr (SBLOCK_OFFS);
> + mapped_sblock = (struct ext2_super_block *) boffs_ptr (SBLOCK_OFFS);
>
> /* Cache a convenient pointer to the block group descriptors for
> allocation.
> These are stored in the filesystem blocks following the superblock. */
> - group_desc_image = (struct ext2_group_desc *) bptr (bptr_block (sblock) +
> 1);
> + group_desc_image =
> + (struct ext2_group_desc *) bptr (bptr_block (mapped_sblock) + 1);
> }
>
> error_t
> @@ -196,8 +198,9 @@ diskfs_set_hypermetadata (int wait, int clean)
> if (sblock_dirty)
> {
> sblock_dirty = 0;
> - disk_cache_block_ref_ptr (sblock);
> - record_global_poke (sblock);
> + memcpy (mapped_sblock, sblock, SBLOCK_SIZE);
> + disk_cache_block_ref_ptr (mapped_sblock);
> + record_global_poke (mapped_sblock);
> }
>
> sync_global (wait);
> --
> 2.0.0.rc0
>
--
Samuel
Progress (n.): The process through which the Internet has evolved from
smart people in front of dumb terminals to dumb people in front of smart
terminals.
