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SubjectRe: [PATCH -mm][preview] memcg: a patch series for next [8/9]
Hi.

I think you are making updated ones, I send comments so far.

On Tue, 19 Aug 2008 17:44:04 +0900, KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote:
> Very experimental...
>
> mem+swap controller prototype.
>
> This patch adds CONFIG_CGROUP_MEM_RES_CTLR_SWAP as memory resource
> controller's swap extension.
>
> When enabling this, memory resource controller will have 2 limits.
>
> - memory.limit_in_bytes .... limit for pages
> - memory.memsw_limit_in_bytes .... limit for pages + swaps.
>
> Following is (easy) accounting state transion after this patch.
>
> pages swaps pages_total memsw_total
> +1 - +1 +1 new page allocation.
> -1 +1 -1 - swap out.
> +1 -1 0 - swap in (*).
> - -1 - -1 swap_free.
>
What do you mean by "pages_total"?

> At swap-out, swp_entry will be charged against the cgroup of the page.
> At swap-in, the page will be charged when it's mapped.
> (Maybe accounting at read_swap() will be beautiful but we can avoid some of
> error handling to delay accounting until mem_cgroup_charge().)
>
> The charge against swap_entry will be uncharged when swap_entry is freed.
>
> The parameter res.swaps just includes swaps not-on swap cache.
> So, this doesn't show real usage of swp_entry just shows swp_entry on disk.
>
IMHO, it would be better to "show" real usage of swp_entry.
Otherwise, "sum of swap usage of all groups" != "swap usage of
system shown by meminfo"(but it means adding another counter, hmm...).

Instead of showing the usage of disk_swap, how about showing
the memsw total usage, which is to be limited by user.

> This patch doesn't include codes for control files.
>
> TODO:
> - clean up. and add comments.
> - support vm_swap_full() under cgroup.
Is it needed?

In my swap controller, swap entries are limited per cgroup.
So, to make swap_cgroup_charge() fail less frequently,
vm_swap_full() should be calculated per cgroup so that
vm can free swap entries in advance.

But I think in mem+swap controller the situation is different.

> - find easier-to-understand protocol....
> - check force_empty....(maybe buggy)
> - support page migration.
> - test!!
>
And,
- move charge along with task move
- hierarchy support

Of course, more basic features and stabilization should be done first.


I agree with this patch as a whole, but I'm worrying about race
between swapout and swapin about the same entry(I should consider more...).


Thanks,
Daisuke Nishimura.


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