Re: [RFC PATCH] powerpc/mm: Reduce memory usage for mm_context_t for radix

[Christophe Leroy]

Le 02/04/2019 à 20:31, Christophe Leroy a écrit :

Le 02/04/2019 à 16:34, Aneesh Kumar K.V a écrit :

Currently, our mm_context_t on book3s64 include all hash specific
context details like slice mask, subpage protection details. We
can skip allocating those on radix. This will help us to save
8K per mm_context with radix translation.

With the patch applied we have

sizeof(mm_context_t)  = 136
sizeof(struct hash_mm_context)  = 8288

Signed-off-by: Aneesh Kumar K.V <aneesh.ku...@linux.ibm.com>
---
NOTE:

If we want to do this, I am still trying to figure out how best we can do this

without all the #ifdef and other overhead for 8xx book3e


  arch/powerpc/include/asm/book3s/64/mmu-hash.h |  2 +-
  arch/powerpc/include/asm/book3s/64/mmu.h      | 48 +++++++++++--------
  arch/powerpc/include/asm/book3s/64/slice.h    |  6 +--
  arch/powerpc/kernel/paca.c                    |  9 ++--
  arch/powerpc/kernel/setup-common.c            |  7 ++-
  arch/powerpc/mm/hash_utils_64.c               | 10 ++--
  arch/powerpc/mm/mmu_context_book3s64.c        | 16 ++++++-
  arch/powerpc/mm/slb.c                         |  2 +-
  arch/powerpc/mm/slice.c                       | 48 +++++++++----------
  arch/powerpc/mm/subpage-prot.c                |  8 ++--
  10 files changed, 91 insertions(+), 65 deletions(-)

[...]

@@ -253,7 +253,7 @@ static void slice_convert(struct mm_struct *mm,
       */
      spin_lock_irqsave(&slice_convert_lock, flags);
-    lpsizes = mm->context.low_slices_psize;
+    lpsizes = mm->context.hash_context->low_slices_psize;

A help to get ->low_slices_psize would help,
something like:

In nohash/32/mmu-8xx:

unsigned char *slice_low_slices_psize(context_t *ctx)
{
     return mm->context.low_slices_psize;

Of course here I meant:

unsigned char *slice_low_slices_psize(mm_context_t *ctx)
{
        return ctx->low_slices_psize;
}

}

And in book3s/64/mmu.h:

unsigned char *slice_low_slices_psize(context_t *ctx)
{
     return mm->context.hash_context->low_slices_psize;

and

unsigned char *slice_low_slices_psize(mm_context_t *ctx)
{
        return ctx->hash_context->low_slices_psize;
}

Christophe