[squid-users] SQUID memory error after vm.swappines changed from 60 to 10

[Bike dernikov1]

On Tue, Nov 14, 2017 at 6:12 PM, Alex Rousskov
<rousskov at measurement-factory.com> wrote:
> On 11/14/2017 08:41 AM, Bike dernikov1 wrote:
>> On Mon, Nov 13, 2017 at 4:36 PM, Alex Rousskov wrote:
>>> On 11/13/2017 02:34 AM, Bike dernikov1 wrote:
>>>> Swap could be used  to translate back data to mem if used, but it
>>>> stays on disk and purge after some time if not used ?
>
>>> The purging bit is wrong. Think of swap as very very very slow RAM.
>
>> So, when squid need something from swap, it will load that data back to ram.
>
> In this context, swap is an OS-level concept. Squid does not know that
> the OS memory manager has swapped some of Squid data from RAM to disk.
> OS does not know what swapped out data means to Squid. When Squid tries
> to access data at a swapped out address, the OS blocks the Squid process
> and loads the missing data from disk into RAM (usually after swapping
> out some RAM bytes to free RAM space for those requested bytes).
>
> Here, "data" essentially means any sequence of bytes allocated by Squid.
> For example, some of those swapped out bytes may have nothing to do with
> Squid memory cache. Swapped out bytes can even be Squid binary code.
>
>
>> For purge, data then  stay in swap forever ?
>
> Swapped out process data stays swapped out until it is either accessed
> by the process (and is swapped in by the OS) or the process terminates
> (without accessing those swapped out bytes). The latter is unlikely for
> Squid data unless the Squid process dies prematurely (i.e., without
> doing internal cleanup).
>
> HTH,
>
> Alex.

Superb explanation. I think that now I understand process much better.

If i can ask under same title:
Yesterday we had error in logs: syslog, cache.log, dmesg,access.log

segfault at 8 ip ....... sp ..... error 4 is squid
process pid exited due to signal 11 with status 0

Squid restarted,  that was at the end of work, and i didn't  notice
change while surfing.
I noticed change in used memory, after i went trough logs, and found segfault.

Can you point me, how to analyze what happened.
Can that be problem with kernel ?

Thanks for help.