[Devel] Re: [PATCH v5 01/14] memcg: Make it possible to use the stock for more than one page.

[Andrew Morton]

On Tue, 16 Oct 2012 14:16:38 +0400
Glauber Costa <glommer at parallels.com> wrote:

> From: Suleiman Souhlal <ssouhlal at FreeBSD.org>
> 
> We currently have a percpu stock cache scheme that charges one page at a
> time from memcg->res, the user counter. When the kernel memory
> controller comes into play, we'll need to charge more than that.
> 
> This is because kernel memory allocations will also draw from the user
> counter, and can be bigger than a single page, as it is the case with
> the stack (usually 2 pages) or some higher order slabs.
> 
> ...
>
> -/*
> - * Try to consume stocked charge on this cpu. If success, one page is consumed
> - * from local stock and true is returned. If the stock is 0 or charges from a
> - * cgroup which is not current target, returns false. This stock will be
> - * refilled.
> +/**
> + * consume_stock: Try to consume stocked charge on this cpu.
> + * @memcg: memcg to consume from.
> + * @nr_pages: how many pages to charge.
> + *
> + * The charges will only happen if @memcg matches the current cpu's memcg
> + * stock, and at least @nr_pages are available in that stock.  Failure to
> + * service an allocation will refill the stock.
> + *
> + * returns true if succesfull, false otherwise.

spello.

>   */
> -static bool consume_stock(struct mem_cgroup *memcg)
> +static bool consume_stock(struct mem_cgroup *memcg, int nr_pages)

I don't believe there is a case for nr_pages < 0 here?  If not then I
suggest that it would be clearer to use an unsigned type, like
memcg_stock_pcp.stock.

>
> ...
>