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Split out the loop that iterates over each batch of FIEMAP
extent data from the function that sets up and calls the ioctl
to reduce nesting and simplify local variable use:
_stats_get_extents_for_file()
-> _stats_map_extents()
The _stats_map_extents() function is responsible for detecting
eof and extent boundaries and adding whole, allocated extents
to the file extent table for region creation.
Check that all region_id values specified in a group bitmap are
actually present: although this should not normally happen when
using the dmstats tool, it is possible as a result of manual
changes (or bugs) for a group descriptor to contain one or more
group_id values that do not exist.
Check for this situation when reading group descriptors, warn
the user the user, and clear these bits in the bitmap when
formatting it for output.
If a region has a a DMS_GROUP tag in aux_data where the first
region_id in the bitmap is not the same as the containing region,
dmstats will segfault:
# '2' is never a valid group bitset list for region_id == 0
# dmsetup message vg_hex/root 0 "@stats_set_aux 0 DMS_GROUP=img:2#"
# dmsetup message vg_hex/root 0 "@stats_list"
0: 45383680+16384 16384 dmstats DMS_GROUP=img:2#
1: 46071808+32768 32768 dmstats -
2: 47382528+16384 16384 dmstats -
# dmstats list
Segmentation fault (core dumped)
The crash will occur in some arbitrary dm_stats_get_* property
method - this happens while processing the 1st region_id in the
bitset, because the region is marked as grouped, but there is
no group bitmap present at dms->groups[2]->regions.
Fix this by detecting a mismatch between the expected region_id
and dm_bit_get_first() for the parsed bitset during
_parse_aux_data_group().
Handle files that contain multiple logical extents in a single
physical extent properly:
- In FIEMAP terms a logical extent is a contiguous range of
sectors in the file's address space.
- One or more physically adjacent logical extents comprise a
physical extent: these are the disk areas that will be mapped
to regions.
- An extent boundary occurs when the start sector of extent
n+1 is not equal to (n.start + n.length).
This requires that we accumulate the length values of extents
returned by FIEMAP until a discontinuity is found (since each
struct fiemap_extent returned by FIEMAP only represents a single
logical extent, which may be contiguous with other logical
extents on-disk).
This avoids creating large numbers of regions for physically
adjacent (logical) extents and fixes the earlier behaviour which
would only map the first logical extent of the physical extent,
leaving gaps in the region table for these files.
To be able to detect lvm2 command is not leaking some
'unexpected' device - remove all devices before
test exits by its own command so test teardown
now can check what was 'left' unexpectedly.
Fix order of operation when converting raid1 into old mirror.
Before any later metadata modification are initiated prepare
mirror_log device with all clearing.
Then directly convert raid1 into mirror with mirror_log.
This convertion now properly see as precommitted metadata
new 'mirror' and committed old 'raid' and is able to
preload all LVs.
When mapping regions to a file descriptor, a temporary table of
extent descriptors is built using the dm_pool object building
interface.
Previously this use borrowed the dms->mem region and counter
table pool (since nothing can interleave with the allocation
while the caller is still in dm_stats_create_regions_from_fd()).
This turns out to be problematic for error recovery. When a
region creation operation fails partway through file mapping,
we need to roll back the set of already created regions and
this requires a listed handle: the dm_stats_list() will then
allocate from the same pool as the extents; we either have
to throw away valid list data, or leak the extent table, to
return the handle in a valid state.
Avoid this problem by creating a new, temporary mem pool in
_stats_create_file_regions() to hold the extent data, and
discarding it on exit from the function.
While cleaning up the table of already created regions during a
failed dm_stats_create_regions_from_fd(), list the handle once,
and call _stats_delete_region() directly. This avoids sending a
@stats_list message for each region deleted, reducing runtime
from 6s to 0.7s when cleaning up ~250 out of ~10000 regions:
# time dmstats create --filemap b.img
device-mapper: message ioctl on (253:0) failed: Cannot allocate memory
Failed to create region 246 of 309 at 9388032.
Could not create regions from file /root/b.img
<< pauses here >>
Command failed
real 0m6.267s
user 0m3.770s
sys 0m2.487s
# time dmstats create --filemap b.img
device-mapper: message ioctl on (253:0) failed: Cannot allocate memory
Failed to create region 246 of 309 at 9388032.
Could not create regions from file /root/b.img
Command failed
real 0m0.716s
user 0m0.034s
sys 0m0.581s
Testing the error path requires region creation to start to
fail part way through the operation (in order to have regions
to clean up): the simplest way is to ensure the system is
close to the kernel limit of 1/4 RAM or 1/2 vmalloc space
consumed by dmstats data.
Split dm_stats_delete_region() so that internal callers can manage
the handle state themselves.
dm_stats_delete_region() now just handles checking the state of the
handle, reporting validation errors, and calling dm_stats_list() if
necessary, before calling _stats_delete_region().
The new _stats_delete_region() function performs the actual group
member removal and region deletion, and requires a fully listed
handle to operate.
Callers that repeatedly delete regions can use a single listed
handle for many operations on the same device, avoiding one
message ioctl per region deleted: since @stats_list with many
regions is expensive, this yields large runtime improvements.
If we fail to create a region during dm_stats_create_regions_from_fd(),
we must remove all regions that were created to do this to date. This
needs to loop over the table of region_id values that were populated
by _stats_create_file_regions() before the error.
The code for this failure case in the out_remove branch incorrectly
uses the table index as the region_id:
for (--i; i != DM_STATS_REGION_NOT_PRESENT; i--) {
if (!dm_stats_delete_region(dms, i))
log_error("Could not delete region " FMTu64 ".", i);
}
This causes the cleanup code to delete a completely unrelated set
of regions (since the index here will always be nr_regions..0).
Fix it to pass the actual region_id stored in regions[i] instead.
Fix a silly bug in dm_stats_delete_region() that hugely inflates
runtimes when deleting a large number of regions.
For ~50,000 regions this change reduces the runtime from 98s to
6s on my test systems (a ~93% reduction).
The bug exists because dm_stats_delete_region() applies a truth
test to the return value of dm_stats_get_nr_areas(); this is
never correct usage - it will walk the entire region table and
calculate area counts for each region (which is roughly O(n^2)
in the number of regions, as dm_stats_delete_region() is being
called inside a region walk).
Although the individual area calculation is not that costly,
uselessly running anything 2,500,000,000 times over gets a bit
slow.
A much cheaper test (which is always true if the areas check is
true) is to just test dm_stats_get_nr_regions() or dms->regions;
if either is true it implies at least one area exists.
Old:
Performance counter stats for 'dmstats delete --allregions --alldevices':
98117.791458 task-clock (msec) # 1.000 CPUs utilized
127 context-switches # 0.001 K/sec
3 cpu-migrations # 0.000 K/sec
6,631 page-faults # 0.068 K/sec
307,711,724,562 cycles # 3.136 GHz
544,762,959,577 instructions # 1.77 insn per cycle
84,287,824,115 branches # 859.047 M/sec
2,538,875 branch-misses # 0.00% of all branches
98.119578733 seconds time elapsed
New:
Performance counter stats for 'dmstats delete --allregions --alldevices':
6427.251074 task-clock (msec) # 1.000 CPUs utilized
6 context-switches # 0.001 K/sec
0 cpu-migrations # 0.000 K/sec
6,634 page-faults # 0.001 M/sec
21,613,018,724 cycles # 3.363 GHz
3,794,755,445 instructions # 0.18 insn per cycle
852,974,026 branches # 132.712 M/sec
808,625 branch-misses # 0.09% of all branches
6.428953647 seconds time elapsed
