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

[Hugh Dickins <hugh@veritas.com>]

On Tue, 18 Nov 2008, Daisuke Nishimura 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.

Excellent find, but ...

> 
> Signed-off-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
> ---
> After this patch, I think memswap controller of x86_32 will be
> on near level with that of x86_64.
> 
>  mm/shmem.c |   23 +++++++++++++++++++++++
>  1 files changed, 23 insertions(+), 0 deletions(-)

... sorry, no, please don't go around unmapping other people's kmaps
like this.  If the memswap controller needs its own kmap_atomic()s at
a level below other users, then it needs to define a new KM_MEMSWAP
in arch/*/include/asm/kmap_types.h and include/asm-*/kmap_types.h.

That's a lot of files which you may not wish to update to get working
right now: I think page_cgroup.c can _probably_ reuse KM_PTE1 as a
temporary measure, but please verify that's safe first.

Hugh

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