Re: [PATCH] zram: keep the exact overcommited value in mem_used_max

From: Minchan Kim
Date: Tue Sep 29 2015 - 21:26:11 EST


On Thu, Sep 24, 2015 at 06:51:52PM +0900, Sergey Senozhatsky wrote:
> From: Sergey SENOZHATSKY <sergey.senozhatsky@xxxxxxxxx>
>
> `mem_used_max' is designed to store the max amount of memory zram
> consumed to store the data. However, it does not represent the actual
> 'overcommited' (max) value. The existing code goes to -ENOMEM
> overcommited case before it updates `->stats.max_used_pages', which
> hides the reason we went to -ENOMEM in the first place -- we actually
> used more memory than `->limit_pages':
>
> alloced_pages = zs_get_total_pages(meta->mem_pool);
> if (zram->limit_pages && alloced_pages > zram->limit_pages) {
> zs_free(meta->mem_pool, handle);
> ret = -ENOMEM;
> goto out;
> }
>
> update_used_max(zram, alloced_pages);
>
> Which is misleading. User will see -ENOMEM, check `->limit_pages',
> check `->stats.max_used_pages', which will keep the value BEFORE zram
> passed `->limit_pages', and see:
> `->stats.max_used_pages' < `->limit_pages'
>
> Move update_used_max() before we do `->limit_pages' check, so that
> user will see:
> `->stats.max_used_pages' > `->limit_pages'
> should the overcommit and -ENOMEM happen.
>
> Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@xxxxxxxxx>

It was intent.

IOW, I want that max_mem_used is never higher than mem_limit but
I realized you are right because user doesn't have way to detect
where -ENOMEM is coming from.
For example, it could come from mem_limit or real memory alloc fail.

Thanks, Sergey.

Acked-by: Minchan Kim <minchan@xxxxxxxxxx>
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/