Bug#799838: linux-image-3.16.0-4-amd64: NFS rename sometimes hangs for 15 seconds
According to Peter Ludikovsky in the debian-user list:
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Am 25.09.2015 um 14:04 schrieb Vincent Lefevre:
> On 2015-09-25 10:11:10 +0200, Peter Ludikovsky wrote:
>> My guess is: Due to the rather large wsize/rsize, the clients
>> create a rather large attribute cache. As a result, when you cat
>> a file on the second machine it updates the atime in the cache,
>> but doesn't yet transfer that information to the server. When you
>> do the mv on the first machine, the client tries to get the
>> current attributes on the files involved, which prompts the
>> server to wait until the second client runs into some kind of
>> timeout and updates the attributes. Only then is the second file
>> "unlocked" to be overwritten.
>>
>> Further proof of that: when setting noatime as a mount option,
>> instead of noac, there's also no delay on the mv.
>
> Thanks for the explanations. But the second client, though it
> doesn't update the attributes immediately, seems to do it quickly
> when asked by the server, otherwise the problem would also be
> visible on Debian 7 machines. I think that on Debian 8, when the
> rename cannot be done immediately, the client retries after 15
> seconds instead of retrying earlier.
>
> Is this related to the following patch?
>
> http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=8478eaa16e701ecfe054b62ec764bc1291b79e19
Can't say if it's related. I have, however, managed to capture the
related network traffic (see attachments).
The big difference happens at packets 58/54 (Deb7/Deb8). For Deb7, the
RENAME call is immediately answered by an NFS4_OK, whereas for Deb8 as
the client it's an NFS4ERR_DELAY. I haven't seen any reason on the
client communication that would explain that, however this is far
beyond my knowledge of the NFS internals.
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See https://lists.debian.org/debian-user/2015/09/msg01120.html for his
message and the attachments.
--
Vincent Lefèvre <vincent@vinc17.net> - Web: <https://www.vinc17.net/>
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Work: CR INRIA - computer arithmetic / AriC project (LIP, ENS-Lyon)
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