Re: [squid-users] Squid Memory and Page Faults

On Thu, Jul 25, 2013 at 06:58:56AM +1200, Amos Jeffries wrote:
> On 25/07/2013 1:05 a.m., Golden Shadow wrote:
> >Hi there!
> >
> >My squid is installed on a server with 192 GB of RAM. I have the following
> >directives in squid.conf:
> >
> >cache_mem 143360 MB
> >maximum_object_size_in_memory 300 KB
> >memory_replacement_policy heap GDSF
> >
> >memory_pools on
> >memory_pools_limit 1024 MB
> >
> >ipcache_size 2048
> >ipcache_low 90
> >ipcache_high 95
> >
> >fqdncache_size 2048
> >
> >
> >
> >top reports that my squid process size is 20GB, which is far less than my
> >RAM size, but nevertheless I still find some page faults (about 70 page
> >faults over 2 hours). I'm wondering how could those page faults are
> >occurring while squid process size is far less than my RAM size. How can I
> >eliminate those time consuming page faults?
>
> Two things here.
>
> Why is the process size only 20GB? you have a 143GB memory cache as part
> of that RAM consumption by Squid. Perhapse your traffics real caching
> requirement is far smaller than you are allowing storage for.
>
>
> What exactly is the page faulting comign from though ... Squid or the OS?
> If it is Squid, why would the OS have swapped that piece of memory out
> to VM in the first place? perhapse something else is needing a chunk of
> memory larger than Squid leaves available?

With plenty of memory and a very large process image, my guess
is that the page fault is a TLB miss and not a swapin.
TLB miss cannot be avoided if a process is larger than the TLB can
address.

Marcus

>
> >My second question, am I using correct values for the memory-related
> >directives mentioned above? If no, I would really appreciate if you could
> >suggest the correct values.
>
> Any values you want are "correct", so long as they fit within the
> machines limits and do not lead to the system swapping.
>
>
> >My last question is about read_ahead_gap, whose default value is only 16
> >KB. Would increasing this value to let's say 32 KB or 64 KB increase the
> >performance since I have high RAM on the server?
>
> Perhapse. That is a buffer size more related to your network speed. Each
> concurrent connection consumes up to that much RAM for buffers. If you
> have clients that can drain 32KB or 64KB fast enough not to cause waves
> or bursts in traffic it can be worthwhile raising it a bit. If you have
> slow clients the reverse can be true.
>
> Amos
Received on Wed Jul 24 2013 - 19:56:35 MDT