RE: [PATCH 8/8] mm/zswap: Use local lock to protect per-CPU data

Song Bao Hua
2020-05-20T12:01:49Z

> Subject: Re: [PATCH 8/8] mm/zswap: Use local lock to protect per-CPU data
>
> On 2020-05-20 11:13:31 [+0000], Song Bao Hua wrote:
> > For example, on cpu1, once you begin to compress, you hold the percpu
> acomp-ctx and percpu destination buffer of CPU1, the below code makes sure
> you get the acomp and dstmem from the same core by disabling preemption
> with get_cpu_var and put_cpu_var:
> > dst = get_cpu_var(zswap_dstmem);
> > acomp_ctx = *this_cpu_ptr(entry->pool->acomp_ctx);
> > put_cpu_var(zswap_dstmem);
> >
> > then there are two cases:
> >
> > 1. after getting dst and acomp_ctx of cpu1, you might always work in cpu1,
> the mutex in per-cpu acomp-ctx will guarantee two compressions won't do at
> the same core in parallel, and it also makes certain compression and
> decompression won't do at the same core in parallel. Everything is like before.
>
> For readability I suggest not to mix per-CPU and per-CTX variables like that. If
> zswap_dstmem is protected by the mutex, please make it part of acomp_ctx.
>

Yep. it seems this will avoid the further explanations to more people who will read the code :-)

> Sebastian

Barry