Re: [squid-users] Re: Linux EXT3 optimizations for Squid

On Sun, 8 Aug 2010 22:32:30 +0200, Heinz Diehl <htd_at_fancy-poultry.org>
wrote:
> On 08.08.2010, Marcus Kool wrote:
>
>> vm.swappiness=20
>> vm.vfs_cache_pressure=50
>
> Do you have some numbers that actually show a significant improvement?
>
> I think at least swappiness should better be 100 here, to free as much
as
> possible memory. Unused applications hanging around for a long
> time can conserve quite a lot of pagecache which otherwise could be used
> actively.

Nope. zero would be better.

The kernel yes, may be optimized to deal with whatever memory it has.

Squid however stores all its caches and index in main memory, along with
hot objects. Each node in the index is 1 page (2 on 64-bit systems) and
every chunk of object data buffered in transfer is 1-2 pages depending on
your allocator. swapping pages in/out for every step across a multi-MB
linked-list or every 4KB of data transfered is not great for performance.
Quite literally the difference between single or triple digits on Squids'
req/sec capacity.

If you have a system which permits individual applications to be prevented
from swapping you can get away with having rarely-used system apps swap
out. But Squid itself must not.

Amos
Received on Sun Aug 08 2010 - 23:26:59 MDT