Re: [PATCH mmotm] memcg: unmap KM_USER0 at shmem_map_and_free_swp if do_swap_account

[KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>]

On Tue, 18 Nov 2008 18:07:21 +0900
Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> wrote:

> memswap controller uses KM_USER0 at swap_cgroup_record and lookup_swap_cgroup.
> 
> But delete_from_swap_cache, which eventually calls swap_cgroup_record, can be
> called with KM_USER0 mapped in case of shmem.
> 
> So it should be unmapped before calling it.
> 
> Signed-off-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Nice Catch!

Thank you for tests and patches.
brief comment below.

> ---
> After this patch, I think memswap controller of x86_32 will be
> on the same level with that of x86_64.
> 
>  mm/shmem.c |   23 +++++++++++++++++++++++
>  1 files changed, 23 insertions(+), 0 deletions(-)
> 
> diff --git a/mm/shmem.c b/mm/shmem.c
> index bee8612..7aebc1b 100644
> --- a/mm/shmem.c
> +++ b/mm/shmem.c
> @@ -171,6 +171,28 @@ static inline void shmem_unacct_size(unsigned long flags, loff_t size)
>  		vm_unacct_memory(VM_ACCT(size));
>  }
>  
> +#if defined(CONFIG_CGROUP_MEM_RES_CTLR_SWAP) && defined(CONFIG_HIGHMEM)
> +/*
> + * memswap controller uses KM_USER0, so dir should be unmapped
> + * before calling delete_from_swap_cache.
> + */
> +static inline void swap_cgroup_map_prepare(struct page ***dir)
> +{
> +	if (!do_swap_account)
> +		return;
> +
> +	if (*dir) {
> +		shmem_dir_unmap(*dir);
> +		*dir = NULL;
> +	}
> +}
> +#else
> +static inline void swap_cgroup_map_prepare(struct page ***dir)
> +{
> +	return;
> +}
> +#endif
> +
>  /*
>   * ... whereas tmpfs objects are accounted incrementally as
>   * pages are allocated, in order to allow huge sparse files.
> @@ -479,6 +501,7 @@ static int shmem_map_and_free_swp(struct page *subdir, int offset,
>  		int size = limit - offset;
>  		if (size > LATENCY_LIMIT)
>  			size = LATENCY_LIMIT;
> +		swap_cgroup_map_prepare(dir);
I think put this before "for() loop" is better.

Thanks,
-Kame

>  		freed += shmem_free_swp(ptr+offset, ptr+offset+size,
>  							punch_lock);
>  		if (need_resched()) {
> 

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