Christophe Leroy's on April 3, 2019 4:31 am:

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

quoted

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 <redacted>
---
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(-)

diff --git a/arch/powerpc/include/asm/book3s/64/mmu-hash.h b/arch/powerpc/include/asm/book3s/64/mmu-hash.h
index a28a28079edb..d801be977623 100644
--- a/arch/powerpc/include/asm/book3s/64/mmu-hash.h
+++ b/arch/powerpc/include/asm/book3s/64/mmu-hash.h

@@ -657,7 +657,7 @@ extern void slb_set_size(u16 size);
  
  /* 4 bits per slice and we have one slice per 1TB */
  #define SLICE_ARRAY_SIZE	(H_PGTABLE_RANGE >> 41)
-#define TASK_SLICE_ARRAY_SZ(x)	((x)->context.slb_addr_limit >> 41)
+#define TASK_SLICE_ARRAY_SZ(x)	((x)->context.hash_context->slb_addr_limit >> 41)
  
  #ifndef __ASSEMBLY__
  

diff --git a/arch/powerpc/include/asm/book3s/64/mmu.h b/arch/powerpc/include/asm/book3s/64/mmu.h
index a809bdd77322..07e76e304a3b 100644
--- a/arch/powerpc/include/asm/book3s/64/mmu.h
+++ b/arch/powerpc/include/asm/book3s/64/mmu.h

@@ -114,6 +114,33 @@ struct slice_mask {
  	DECLARE_BITMAP(high_slices, SLICE_NUM_HIGH);
  };
  
+struct hash_mm_context {
+
+	u16 user_psize; /* page size index */

Could we keep that in mm_context_t ?

Why do you want it there?

quoted

@@ -155,15 +155,15 @@ static struct slice_mask *slice_mask_for_size(struct mm_struct *mm, int psize)
  {
  #ifdef CONFIG_PPC_64K_PAGES
  	if (psize == MMU_PAGE_64K)
-		return &mm->context.mask_64k;
+		return &mm->context.hash_context->mask_64k;

You should take the two patches below, that would help:
https://patchwork.ozlabs.org/patch/1059056/
https://patchwork.ozlabs.org/patch/1059058/

Above patches seem good I think. What I think Aneesh should have is
is a macro or inline that gives a pointer to the hash_mm_context from
an mm_context pointer.

Architectures which always want it should just put the hash struct
in their mm_context struct and that avoids the pointer overhead
completely.

Thanks,
Nick