Re: [PATCH] rpc: RH1026137: Fix slow volume download (virsh vol-download)

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On Mon, Jul 20, 2015 at 05:42:11PM +0300, Ossi Herrala wrote:
On Sat, Jun 06, 2015 at 07:36:48PM +0000, Ossi Herrala wrote:

Sorry to miss this mail, it got buried somehow and I haven't got to it
until now since nobody pinged it.  Sorry for the long wait then.


No worries and thank you for taking time to review my patch. See new
patch attached as well as comments on the memory usage below.

The patch is tested on latest master (e46791e003444ce825feaf5bb2a16f778ee951e5).


The only thing I would mention wrt to how it works after this patch is
that it will consume some memory that's not needed, precisely
(sizeof(struct iovec) + sizeof(void *)) * unreadMBs.  It might be
worth it to do:

 memmove(st->incomingVec, st->incomingVec + st->readVec,
         st->writeVec - st->readVec);
 VIR_SHRINK_N(st->incomingVec, st->readVec);
 st->writeVec -= st->readVec;
 st->readVec = 0;

Apart from that it's definitely *way* better approach.  What do you
think of such modification?  This would go either instead
'st->readVec++', but rather at the end of this function, so it's not
done after each MB read.


I totally agree and implemented freeing of the memory in the new
patch:

 if (st->readVec >= 16) {
   memmove(st->incomingVec, st->incomingVec + st->readVec,
           sizeof(*st->incomingVec)*(st->writeVec - st->readVec));
   VIR_SHRINK_N(st->incomingVec, st->writeVec, st->readVec);
   VIR_DEBUG("shrink removed %zu, left %zu", st->readVec, st->writeVec);
   st->readVec = 0;
 }

now it only frees memory in chunks of 16 to avoid doing memmove() all
the time. The iovec is 16 bytes (in 64 bit Linux) so this frees 256
bytes at a time and in my testing usually everything or almost
everything that is allocated.


Thanks again for taking time to review and commit, and I hope the new
patch below is formatted ok.


I managed to apply it as needed.  I like how it works now and the
feeing is fine, too.  I tested it and it seems it's working perfectly.
Without this patch I've got stuck on 1MiB/s locally after 11GiB in
circa 1 minute, with this patch I managed to download 20GiB in less
than a minute.

ACK && will push after release since we're way after rc2 already.

Again, sorry for the delays and thanks for the contribution!

Have a nice day,
Martin

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