On 4/7/21 12:01 PM, Olga Kornievskaia wrote:
On Wed, Apr 7, 2021 at 1:13 PM <dai.ngo@xxxxxxxxxx> wrote:
On 4/7/21 9:30 AM, Olga Kornievskaia wrote:
On Tue, Apr 6, 2021 at 9:23 PM <dai.ngo@xxxxxxxxxx> wrote:
On 4/6/21 6:12 PM, dai.ngo@xxxxxxxxxx wrote:
On 4/6/21 1:43 PM, Olga Kornievskaia wrote:
On Tue, Apr 6, 2021 at 3:58 PM Chuck Lever III
<chuck.lever@xxxxxxxxxx> wrote:
On Apr 6, 2021, at 3:57 PM, Olga Kornievskaia
<olga.kornievskaia@xxxxxxxxx> wrote:
On Tue, Apr 6, 2021 at 3:43 PM Chuck Lever III
<chuck.lever@xxxxxxxxxx> wrote:
On Apr 6, 2021, at 3:41 PM, Olga Kornievskaia
<olga.kornievskaia@xxxxxxxxx> wrote:
On Tue, Apr 6, 2021 at 12:33 PM Chuck Lever III
<chuck.lever@xxxxxxxxxx> wrote:
On Apr 2, 2021, at 7:30 PM, Dai Ngo <dai.ngo@xxxxxxxxxx> wrote:
Hi,
Currently the source's export is mounted and unmounted on every
inter-server copy operation. This causes unnecessary overhead
for each copy.
This patch series is an enhancement to allow the export to remain
mounted for a configurable period (default to 15 minutes). If the
export is not being used for the configured time it will be
unmounted
by a delayed task. If it's used again then its expiration time is
extended for another period.
Since mount and unmount are no longer done on each copy request,
this overhead is no longer used to decide whether the copy should
be done with inter-server copy or generic copy. The threshold used
to determine sync or async copy is now used for this decision.
-Dai
v2: fix compiler warning of missing prototype.
Hi Olga-
I'm getting ready to shrink-wrap the initial NFSD v5.13 pull
request.
Have you had a chance to review Dai's patches?
Hi Chuck,
I apologize I haven't had the chance to review/test it yet. Can I
have
until tomorrow evening to do so?
Next couple of days will be fine. Thanks!
I also assumed there would be a v2 given that kbot complained about
the NFSD patch.
This is the v2 (see Subject: )
Sigh. Thank you. I somehow missed v2 patches themselves and only saw
the originals. Again I'll test/review the v2 by the end of the day
tomorrow!
Actually a question for Dai: have you done performance tests with your
patches and can show that small copies still perform? Can you please
post your numbers with the patch series? When we posted the original
patch set we did provide performance numbers to support the choices we
made (ie, not hurting performance of small copies).
Currently the source and destination export was mounted with default
rsize of 524288 and the patch uses threshold of (rsize * 2 = 1048576)
to decide whether to do inter-server copy or generic copy.
I ran performance tests on my test VMs, with and without the patch,
using 4 file sizes 1048576, 1049490, 2048000 and 7341056 bytes. I ran
each test 5 times and took the average. I include the results of 'cp'
for reference:
size cp with patch without patch
----------------------------------------------------------------
1048576 0.031 0.032 (generic) 0.029 (generic)
1049490 0.032 0.042 (inter-server) 0.037 (generic)
2048000 0.051 0.047 (inter-server) 0.053 (generic)
7341056 0.157 0.074 (inter-server) 0.185 (inter-server)
----------------------------------------------------------------
Sorry, times are in seconds.
Thank you for the numbers. #2 case is what I'm worried about.
Regarding performance numbers, the patch does better than the original
code in #3 and #4 and worse then original code in #1 and #2. #4 run
shows the benefit of the patch when doing inter-copy. The #2 case can
be mitigated by using a configurable threshold. In general, I think it's
more important to have good performance on large files than small files
when using inter-server copy. Note that the original code does not
do well with small files either as shown above.
I think the current approach tries to be very conservative to achieve
the goal of never being worse than the cp. I'm not sure what you mean
that current code doesn't do well with small files. For small files it
falls back to the generic copy.
In this table, the only advantage the current code has over 'cp' is
run 1 which I don't know why. The rest is slower than 'cp'. I don't
have the size of the copy where the inter-copy in the current code
starts showing better performance yet, but even at ~7MB it is still
slower than 'cp'. So for any size that is smaller than 7MB+, the
inter-server copy will be slower than 'cp'. Compare that with the
patch, the benefit of inter-server copy starts at ~2MB.
I don't believe the code works. In my 1st test doing "nfstest_ssc
--runtest inter01" and then doing it again. What I see from inspecting
the traces is that indeed unmount doesn't happen but for the 2nd copy
the mount happens again.
I'm attaching the trace. my servers are .114 (dest), .110 (src). my
client .68. The first run of "inter01" places a copy in frame 364.
frame 367 has the beginning of the "mount" between .114 and .110. then
read happens. then a copy offload callback happens. No unmount happens
as expected. inter01 continues with its verification and clean up. By
frame 768 the test is done. I'm waiting a bit. So there is a heatbeat
between the .114 and .110 in frame 769. Then the next run of the
"inter01", COPY is placed in frame 1110. The next thing that happens
are PUTROOTFH+bunch of GETATTRs that are part of the mount. So what is
the saving here? a single EXCHANGE_ID? Either the code doesn't work or
however it works provides no savings.
The saving are EXCHANGE_ID, CREATE_SESSION, RECLAIM COMPLETE,
DESTROY_SESSION and DESTROY_CLIENTID for *every* inter-copy request.
The saving is reflected in the number of #4 test run above.
Can't we do better than that? Since you are keeping a list of umounts,
can't they be searched before doing the vfs_mount() and instead get
the mount structure from the list (and not call the vfs_mount at all)
and remove it from the umount list (wouldn't that save all the calls)?
I thought about this. My problem here is that we don't have much to key
on to search the list. The only thing in the COPY argument can be used
for this purpose is the list of IP addresses of the source server.
I think that is not enough, there can be multiple exports from the
same server, how do we find the right one? it can get complicated.
I'm happy to consider any suggestion you have for this.
I think the patch is an improvement, in performance for copying large
files (if you consider 2MB file is large) and for removing the bug
of computing overhead in __nfs4_copy_file_range. Note that we can
always improve it and not necessary doing it all at once.
-Dai
Note that the overhead of the copy in the current code includes mount
*and* unmount. However the threshold computed in __nfs4_copy_file_range
includes only the guesstimated mount overhead and not the unmount
overhead so it not correct.
-Dai
Honestly I don't understand the whole need of a semaphore and all.
The semaphore is to prevent the export to be unmounted while it's
being used.
-Dai
My
approach that I tried before was to create a delayed work item but I
don't recall why I dropped it.
https://urldefense.com/v3/__https://patchwork.kernel.org/project/linux-nfs/patch/20170711164416.1982-43-kolga@xxxxxxxxxx/__;!!GqivPVa7Brio!Jl5Wq7nrFUsaUQjgLJoSuV-cDlvbPaav3x8nXQcRhAdxjVEoWvK24sNgoE82Zg$
-Dai
Note that without the patch, the threshold to do inter-server
copy is (524288 * 14 = 7340032) bytes. With the patch, the threshold
to do inter-server is (524288 * 2 = 1048576) bytes, same as
threshold to decide to sync/async for intra-copy.
While I agree that delaying the unmount on the server is beneficial
I'm not so sure that dropping the client restriction is wise because
the small (singular) copy would suffer the setup cost of the initial
mount.
Right, but only the 1st copy. The export remains to be mounted for
15 mins so subsequent small copies do not incur the mount and unmount
overhead.
I think ideally we want the server to do inter-copy only if it's faster
than the generic copy. We can probably come up with a number after some
testing and that number can not be based on the rsize as it is now since
the rsize can be changed by mount option. This can be a fixed number,
1M/2M/etc, and it should be configurable. What do you think? I'm open
to any other options.
Just my initial thoughts...
Thanks,
-Dai
--
Chuck Lever
