This feature is especially useful for better understanding how e2fsprogs
tools (mainly e2fsck) treats bitmaps and what bitmap backend can be most
suitable for particular bitmap. Backend itself (if implemented) can
provide statistics of its own as well.
[ Changed to provide basic statistics when enabled with the
E2FSPROGS_BITMAPS_STATS environment variable -- tytso]
Signed-off-by: Lukas Czerner <lczerner@redhat.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
For a long time we had a bitarray backend for storing filesystem
metadata bitmaps, however today this approach might hit its limits with
todays huge data storage devices, because of its memory utilization.
Bitarrays stores bitmaps as ..well, as bitmaps. But this is in most
cases highly unefficient because we need to allocate memory even for the
big parts of bitmaps we will never use, resulting in high memory
utilization especially for huge filesystem, when bitmaps might occupy
gigabytes of space.
This commit adds another backend to store bitmaps. It is based on
rbtrees and it stores just used extents of bitmaps. It means that it can
be more memory efficient in most cases.
I have done some limited benchmarking and it shows that rbtree backend
consumes approx 65% less memory that bitarray on 312GB filesystem aged
with Impression (default config). This number may grow significantly
with the filesystem size, but also it may be a lot lower (even negative)
if the inodes are very fragmented (need more benchmarking).
This commit itself does not enable the use of rbtree backend.
[ Simplified the code by avoiding unneeded memory allocation and
deallocation of del_ext. In addition, fixed a bug discovered by the
tst_bitmaps tests: rb_unamrk_bmap() must return true if the bit was
previously set in bitmap, and zero otherwise -- tytso ]
Signed-off-by: Lukas Czerner <lczerner@redhat.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
This patch makes the following changes:
* ext2fs_allocate_block_bitmap() now allocates a bitmap with cluster
granularity for bigalloc file systems. For mke2fs and e2fsck, a
newly added function, ext2fs_allocate_subcluster_bitmap() allocates
a bitmap with block granularity (even for bigalloc file systems).
The newly added function ext2fs_get_bitmap_granularity() will return
the number of bits (log2) of the granularity used by the bitmap.
* The ext2fs_{mark,unmark,test}_block_bitmap2() functions will shift
their passed-in argument by log2(cluster_ganularity) bits right.
This means that the arguments for the single-argument bitmap
functions will be interpreted with block granluarity, since this
minimizes code changes in the rest of the code base.
* The ext2fs_{get,set}_block_bitmap_range() functions will interpret
their arguments in cluster granularity. This is a bit inconsistent,
but the caller of those functions will need to be taught about the
subtleties of clusters for bigalloc file systems.
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Initial design was done by Theodore Ts'o; implementation was fleshed
out by Valerie Aurora Henson. Also includes some fixes from Nick Dokos.
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Signed-off-by: Valerie Aurora Henson <vaurora@redhat.com>
Signed-off-by: Nick Dokos <nicholas.dokos@hp.com>
Lukas Czerner