Re: access to hard drives is "blocked" by writes to a flash driv

On 03/02/2013 21:46, Edward Tomasz Napiera=B3a wrote:
> Wiadomo=B6=E6 napisana przez deeptech71 w dniu 2 mar 2013, o godz. 18:29:
>> When one of my flash drives is being heavily written to; typically by ``=
svn update'' on /usr/src, located on the flash drive; the following can be =
said about filesystem behavior:
>>
>> - ``svn update'' seems to be able to quickly update a bunch of files, bu=
t is then unable to continue for a period of time. This behavior is cyclica=
l, and cycles several times, depending on the amount of updating work to be=
 done for a particular run of ``svn update''.
>> - Access to any filesystem, whether on the said flash drive or not, seem=
s to be hindered a lot, typically during the said "unable to continue" time=
.. Reading of a file on a hard drive was once delayed for more than 10 secon=
ds. Seemingly as a consequence, the starting of top(1) is also typically de=
layed.
>
> When that happens, could you do "ps axl" and see the WCHAN column
> for the affected processes?  Is it "wdrain"?

What do you mean by "the affected processes"?

The MWCHAN of an ``svn update'' contained long "wdrain" periods (but includ=
ed "getblk", "drainvp", etc.). ``[bufdaemon]'' sometimes seemed to somewhat=
 follow the "wdrain" state of ``svn update''.

I've also found out that the inability for top(1) or ps(1) to start immedia=
tely has something to do with X -- in the virtual terminals, there was neve=
r a delay.
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