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6e1d7276c9
Based on the comments in arc.c we know that buffers can exist both
in arc and l2arc, under this circumstance both arc_buf_hdr_t and
l2arc_buf_hdr_t will be allocated. However the current logic only
cares for memory that l2arc_buf_hdr takes up when the buffer's
state transfers from or to arc_l2c_only. This will cause obvious
deviations for illumos's zfs version since the sizeof(l2arc_buf_hdr)
is larger than ZOL's. We can implement the calcuation in the
following simple way:
1. When allocate a l2arc_buf_hdr_t we add its memory consumption
instantly and subtract it when we free or evict the l2arc buf.
2. According to l2arc_hdr_stat_add and l2arc_hdr_stat_remove, if
the buffer only stays in l2arc we should also add the memory
its arc_buf_hdr_t consumes, so we only need to add HDR_SIZE to
arcstat_l2_hdr_size since we already concerned with L2HDR_SIZE
in step 1 and the same for transfering arc bufs from l2arc only
state.
The testbox has 2 4-core Intel Xeon CPUs(2.13GHz), with 16GB memory
and tests were set upped in the following way:
1. Fdisked a SATA disk into two partitions, one partition for zpool
storage and the other one was used as the cache device.
2. Generated some files occupying 14GB altogether in the zpool
prepared in step 1 using iozone.
3. Read them all using md5sum and watched the l2arc related statistics
in /proc/spl/kstat/zfs/arcstats. After the reading ended the
l2_hdr_size and l2_size were shown like this:
l2_size 4 4403780608
l2_hdr_size 4 0
which was weird.
4. After applying this patch and reran step 1-3, the results were
as following:
l2_size 4 4306443264
l2_hdr_size 4 535600
these numbers made sense, on 64-bit systems the
sizeof(l2arc_buf_hdr_t) is 16 bytes. Assue all blocks cached by
l2arc are 128KB, so 535600/16*128*1024=4387635200, since not all
blocks are equal-sized, the theoretical result will be a little
bigger, as we can see.
Since I'm familiar with systemtap instrumentation tool I used it to
examine what had happened. The script looked like this:
probe module("zfs").function("arc_chage_state")
{
if ($new_state == $arc_l2_only)
printf("change arc buf to arc_l2_only\n")
}
It will print out some information each time we call funciton
arc_chage_state if the argument new_state is arc_l2_only. I
gathered the trace logs and found that none of the arc bufs ran
into arc state arc_l2_only when the tests was running, this was
the reason why l2_hdr_size in step 3 was 0. The arc bufs fell into
arc_l2_only when the pool or the filesystem was offlined.
Signed-off-by: Ying Zhu <casualfisher@gmail.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
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| config | ||
| dracut | ||
| etc | ||
| include | ||
| lib | ||
| man | ||
| module | ||
| patches | ||
| rpm | ||
| scripts | ||
| udev | ||
| .gitignore | ||
| AUTHORS | ||
| autogen.sh | ||
| configure.ac | ||
| copy-builtin | ||
| COPYRIGHT | ||
| DISCLAIMER | ||
| Makefile.am | ||
| META | ||
| OPENSOLARIS.LICENSE | ||
| README.markdown | ||
| zfs-script-config.sh.in | ||
| zfs.release.in | ||
Native ZFS for Linux!
ZFS is an advanced file system and volume manager which was originally developed for Solaris and is now maintained by the Illumos community.
ZFS on Linux, which is also known as ZoL, is currently feature complete. It includes fully functional and stable SPA, DMU, ZVOL, and ZPL layers.
Full documentation for installing ZoL on your favorite Linux distribution can be found at: http://zfsonlinux.org