Re: [External] Re: [RFC PATCH 1/3] zram: charge the compressed RAM to the page's memcgroup

[David Hildenbrand]

On 15.06.23 13:15, 贺中坤 wrote:
> On Thu, Jun 15, 2023 at 5:27 PM David Hildenbrand <david@xxxxxxxxxx> wrote:
> > Interesting. When looking at possible ways to achieve that in a clean
> > way, my understanding was that the page might not always be accounted to
> > a memcg (e.g., simply some buffer?). Besides the swap->zram case I was
> > thinking about other fs->zram case, or just a straight read/write to the
> > zram device.
> >
> > The easiest way to see where that goes wrong I think is
> > zram_bvec_write_partial(), where we simply allocate a temporary page.
> >
> > Either I am missing something important, or this only works in some
> > special cases.
> >
> > I came to the conclusion that the only reasonable way is to assign a
> > complete zram device to a single cgroup and have all memory accounted to
> > that cgroup. Does also not solve all use cases (especially the
> > swap->zram case that might be better offjust using zswap?) but at least
> > the memory gets accounted in a more predictable way.
> >
> > Happy to learn more.
> >
> > --
> > Cheers,
> >
> > David / dhildenb
>
> Hi david, thanks for your reply. This should be my mistake, I didn't
> describe the
> problem clearly.
>
> The reason for the problem is not the temporary page allocated at the beginning
> of zram_bvec_write_partial() and released at the end,but the compressed memory
> allocated by zs_malloc() in zram_write_page().
>
> So, it may not meet the need to  assign a complete zram device to a
> single cgroup.
> we need to charge the compressed memory to the original page's memory cgroup,
> which is not charged so far.

Yes, but my point is that there are cases where the pages you get are 
not charged. zram_bvec_write_partial() is just one such example that 
highlights the issue.

--
Cheers,

David / dhildenb