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Re: [PATCH] Shrink the size of tlb handler

To: Wu Fei <at.wufei@gmail.com>, Ralf Baechle <ralf@linux-mips.org>
Subject: Re: [PATCH] Shrink the size of tlb handler
From: David Daney <ddaney@caviumnetworks.com>
Date: Wed, 09 Sep 2009 15:36:35 -0700
Cc: linux-mips@linux-mips.org
In-reply-to: <20090903142953.GB6482@desktop>
Original-recipient: rfc822;linux-mips@linux-mips.org
References: <20090903142753.GA6482@desktop> <20090903142953.GB6482@desktop>
Sender: linux-mips-bounce@linux-mips.org
User-agent: Thunderbird 2.0.0.21 (X11/20090320)
Wu Fei wrote:
By combining swapper_pg_dir and module_pg_dir, several if conditions
can be eliminated from the tlb exception handler. The reason they
can be combined is that, the effective virtual address of vmalloc
returned is at the bottom, and of module_alloc returned is at the
top. It also fixes the bug in vmalloc(), which happens when its
return address is not covered by the first pgd.

Signed-off-by: Wu Fei <at.wufei@gmail.com>


I like this patch. I ported it to my 2.6.27 kernel and it seems to work well.

One thing you are missing is that that label_module_alloc should now no longer be needed in tlbex.c It should be removed.

David Daney


---
 arch/mips/include/asm/pgtable-64.h |   11 ++------
 arch/mips/mm/init.c                |    3 --
 arch/mips/mm/pgtable-64.c          |    3 --
 arch/mips/mm/tlbex.c               |   49 ------------------------------------
 4 files changed, 3 insertions(+), 63 deletions(-)

diff --git a/arch/mips/include/asm/pgtable-64.h 
b/arch/mips/include/asm/pgtable-64.h
index 4ed9d1b..9cd5089 100644
--- a/arch/mips/include/asm/pgtable-64.h
+++ b/arch/mips/include/asm/pgtable-64.h
@@ -109,13 +109,13 @@
#define VMALLOC_START MAP_BASE
 #define VMALLOC_END    \
-       (VMALLOC_START + PTRS_PER_PGD * PTRS_PER_PMD * PTRS_PER_PTE * PAGE_SIZE)
+       (VMALLOC_START + \
+        PTRS_PER_PGD * PTRS_PER_PMD * PTRS_PER_PTE * PAGE_SIZE - (1UL << 32))
 #if defined(CONFIG_MODULES) && defined(KBUILD_64BIT_SYM32) && \
        VMALLOC_START != CKSSEG
 /* Load modules into 32bit-compatible segment. */
 #define MODULE_START   CKSSEG
 #define MODULE_END     (FIXADDR_START-2*PAGE_SIZE)
-extern pgd_t module_pg_dir[PTRS_PER_PGD];
 #endif
#define pte_ERROR(e) \
@@ -188,12 +188,7 @@ static inline void pud_clear(pud_t *pudp)
 #define __pmd_offset(address)  pmd_index(address)
/* to find an entry in a kernel page-table-directory */
-#ifdef MODULE_START
-#define pgd_offset_k(address) \
-       ((address) >= MODULE_START ? module_pg_dir : pgd_offset(&init_mm, 0UL))
-#else
-#define pgd_offset_k(address) pgd_offset(&init_mm, 0UL)
-#endif
+#define pgd_offset_k(address) pgd_offset(&init_mm, address)
#define pgd_index(address) (((address) >> PGDIR_SHIFT) & (PTRS_PER_PGD-1))
 #define pmd_index(address)     (((address) >> PMD_SHIFT) & (PTRS_PER_PMD-1))
diff --git a/arch/mips/mm/init.c b/arch/mips/mm/init.c
index 0e82050..38c79c5 100644
--- a/arch/mips/mm/init.c
+++ b/arch/mips/mm/init.c
@@ -475,9 +475,6 @@ unsigned long pgd_current[NR_CPUS];
  */
 pgd_t swapper_pg_dir[_PTRS_PER_PGD] __page_aligned(_PGD_ORDER);
 #ifdef CONFIG_64BIT
-#ifdef MODULE_START
-pgd_t module_pg_dir[PTRS_PER_PGD] __page_aligned(PGD_ORDER);
-#endif
 pmd_t invalid_pmd_table[PTRS_PER_PMD] __page_aligned(PMD_ORDER);
 #endif
 pte_t invalid_pte_table[PTRS_PER_PTE] __page_aligned(PTE_ORDER);
diff --git a/arch/mips/mm/pgtable-64.c b/arch/mips/mm/pgtable-64.c
index e4b565a..1121019 100644
--- a/arch/mips/mm/pgtable-64.c
+++ b/arch/mips/mm/pgtable-64.c
@@ -59,9 +59,6 @@ void __init pagetable_init(void)
/* Initialize the entire pgd. */
        pgd_init((unsigned long)swapper_pg_dir);
-#ifdef MODULE_START
-       pgd_init((unsigned long)module_pg_dir);
-#endif
        pmd_init((unsigned long)invalid_pmd_table, (unsigned 
long)invalid_pte_table);
pgd_base = swapper_pg_dir;
diff --git a/arch/mips/mm/tlbex.c b/arch/mips/mm/tlbex.c
index 9a17bf8..bc66f57 100644
--- a/arch/mips/mm/tlbex.c
+++ b/arch/mips/mm/tlbex.c
@@ -499,11 +499,7 @@ build_get_pmde64(u32 **p, struct uasm_label **l, struct 
uasm_reloc **r,
         * The vmalloc handling is not in the hotpath.
         */
        uasm_i_dmfc0(p, tmp, C0_BADVADDR);
-#ifdef MODULE_START
-       uasm_il_bltz(p, r, tmp, label_module_alloc);
-#else
        uasm_il_bltz(p, r, tmp, label_vmalloc);
-#endif
        /* No uasm_i_nop needed here, since the next insn doesn't touch TMP. */
#ifdef CONFIG_SMP
@@ -556,52 +552,7 @@ build_get_pgd_vmalloc64(u32 **p, struct uasm_label **l, 
struct uasm_reloc **r,
 {
        long swpd = (long)swapper_pg_dir;
-#ifdef MODULE_START
-       long modd = (long)module_pg_dir;
-
-       uasm_l_module_alloc(l, *p);
-       /*
-        * Assumption:
-        * VMALLOC_START >= 0xc000000000000000UL
-        * MODULE_START >= 0xe000000000000000UL
-        */
-       UASM_i_SLL(p, ptr, bvaddr, 2);
-       uasm_il_bgez(p, r, ptr, label_vmalloc);
-
-       if (uasm_in_compat_space_p(MODULE_START) &&
-           !uasm_rel_lo(MODULE_START)) {
-               uasm_i_lui(p, ptr, uasm_rel_hi(MODULE_START)); /* delay slot */
-       } else {
-               /* unlikely configuration */
-               uasm_i_nop(p); /* delay slot */
-               UASM_i_LA(p, ptr, MODULE_START);
-       }
-       uasm_i_dsubu(p, bvaddr, bvaddr, ptr);
-
-       if (uasm_in_compat_space_p(modd) && !uasm_rel_lo(modd)) {
-               uasm_il_b(p, r, label_vmalloc_done);
-               uasm_i_lui(p, ptr, uasm_rel_hi(modd));
-       } else {
-               UASM_i_LA_mostly(p, ptr, modd);
-               uasm_il_b(p, r, label_vmalloc_done);
-               if (uasm_in_compat_space_p(modd))
-                       uasm_i_addiu(p, ptr, ptr, uasm_rel_lo(modd));
-               else
-                       uasm_i_daddiu(p, ptr, ptr, uasm_rel_lo(modd));
-       }
-
        uasm_l_vmalloc(l, *p);
-       if (uasm_in_compat_space_p(MODULE_START) &&
-           !uasm_rel_lo(MODULE_START) &&
-           MODULE_START << 32 == VMALLOC_START)
-               uasm_i_dsll32(p, ptr, ptr, 0);  /* typical case */
-       else
-               UASM_i_LA(p, ptr, VMALLOC_START);
-#else
-       uasm_l_vmalloc(l, *p);
-       UASM_i_LA(p, ptr, VMALLOC_START);
-#endif
-       uasm_i_dsubu(p, bvaddr, bvaddr, ptr);
if (uasm_in_compat_space_p(swpd) && !uasm_rel_lo(swpd)) {
                uasm_il_b(p, r, label_vmalloc_done);


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