Re: [patch] pae-2.4.3-A4

Ingo Molnar
2001-03-25T18:51:13Z

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On Sun, 25 Mar 2001, Linus Torvalds wrote:

> So my suggestion for PAE is:
>
> - populate in gdb_alloc() (ie just do the three "alloc_page()" calls to
> allocate the PMD's immediately)
>
> NOTE: This makes the race go away, and will actually speed things up as
> we will pretty much in practice always populate the PGD _anyway_, the
> way the VM areas are laid out.
>
> - make "pgd_present()" always return 1.
>
> NOTE: This will speed up the page table walkers anyway. It will also
> avoid the problem above.
>
> - make "free_pmd()" a no-op.
>
> All of the above will (a) simplify things (b) remove special cases and
> (c) remove actual and existing bugs.

yep, this truly makes things so much easier and cleaner! There was only
one thing missing to make it work:

- make "pgd_clear()" a no-op.

[the reason for the slightly more complex pgd_alloc_slow() code is to
support non-default virtual memory splits as well, where the number of
user pgds is not necesserily 3.]

plus i took to opportunity to reduce the allocation size of PAE-pgds.
Their size is only 32 bytes, and we allocated a full page. Now the code
kmalloc()s a 32 byte cacheline for the pgd. (there is a hardware
constraint on alignment: this cacheline must be at least 16-byte aligned,
which is true for the current kmalloc() code.) So the per-process cost is
reduced by almost 4 KB.

and i got rid of pgalloc-[2|3]level.h - with the pmds merged into the pgd
logic the algorithmic difference between 2-level and this pseudo-3-level
PAE paging is not that big anymore. The pgtable-[2|3]level.h files are
still separate.

the attached pae-2.4.3-B2 patch (against 2.4.3-pre7) compiles & boots just
fine both in PAE and non-PAE mode. The patch removes 217 lines, and adds
only 78 lines.

Ingo

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--- linux/include/asm-i386/pgalloc-3level.h.orig Sun Mar 25 18:55:05 2001
+++ linux/include/asm-i386/pgalloc-3level.h Sun Mar 25 22:38:41 2001
@@ -1,45 +0,0 @@
-#ifndef _I386_PGALLOC_3LEVEL_H
-#define _I386_PGALLOC_3LEVEL_H
-
-/*
- * Intel Physical Address Extension (PAE) Mode - three-level page
- * tables on PPro+ CPUs. Page-table allocation routines.
- *
- * Copyright (C) 1999 Ingo Molnar <mingo@redhat.com>
- */
-
-extern __inline__ pmd_t *pmd_alloc_one(void)
-{
- pmd_t *ret = (pmd_t *)__get_free_page(GFP_KERNEL);
-
- if (ret)
- memset(ret, 0, PAGE_SIZE);
- return ret;
-}
-
-extern __inline__ pmd_t *pmd_alloc_one_fast(void)
-{
- unsigned long *ret;
-
- if ((ret = pmd_quicklist) != NULL) {
- pmd_quicklist = (unsigned long *)(*ret);
- ret[0] = 0;
- pgtable_cache_size--;
- } else
- ret = (unsigned long *)get_pmd_slow();
- return (pmd_t *)ret;
-}
-
-extern __inline__ void pmd_free_fast(pmd_t *pmd)
-{
- *(unsigned long *)pmd = (unsigned long) pmd_quicklist;
- pmd_quicklist = (unsigned long *) pmd;
- pgtable_cache_size++;
-}
-
-extern __inline__ void pmd_free_slow(pmd_t *pmd)
-{
- free_page((unsigned long)pmd);
-}
-
-#endif /* _I386_PGALLOC_3LEVEL_H */
--- linux/include/asm-i386/pgalloc.h.orig Sun Mar 25 18:56:25 2001
+++ linux/include/asm-i386/pgalloc.h Sun Mar 25 23:11:23 2001
@@ -11,37 +11,56 @@
#define pte_quicklist (current_cpu_data.pte_quick)
#define pgtable_cache_size (current_cpu_data.pgtable_cache_sz)

-#define pmd_populate(pmd, pte) set_pmd(pmd, __pmd(_PAGE_TABLE + __pa(pte)))
-
-#if CONFIG_X86_PAE
-# include <asm/pgalloc-3level.h>
-#else
-# include <asm/pgalloc-2level.h>
-#endif
+#define pmd_populate(pmd, pte) \
+ set_pmd(pmd, __pmd(_PAGE_TABLE + __pa(pte)))

/*
- * Allocate and free page tables. The xxx_kernel() versions are
- * used to allocate a kernel page table - this turns on ASN bits
- * if any.
+ * Allocate and free page tables.
*/

+#if CONFIG_X86_PAE
+
+extern void *kmalloc(size_t, int);
+extern void kfree(const void *);
+
extern __inline__ pgd_t *get_pgd_slow(void)
{
- pgd_t *ret = (pgd_t *)__get_free_page(GFP_KERNEL);
+ int i;
+ pgd_t *pgd = kmalloc(PTRS_PER_PGD * sizeof(pgd_t), GFP_KERNEL);
+
+ if (pgd) {
+ for (i = 0; i < USER_PTRS_PER_PGD; i++) {
+ unsigned long pmd = __get_free_page(GFP_KERNEL);
+ if (!pmd)
+ goto out_oom;
+ clear_page(pmd);
+ set_pgd(pgd + i, __pgd(1 + __pa(pmd)));
+ }
+ memcpy(pgd + USER_PTRS_PER_PGD, swapper_pg_dir + USER_PTRS_PER_PGD, (PTRS_PER_PGD - USER_PTRS_PER_PGD) * sizeof(pgd_t));
+ }
+ return pgd;
+out_oom:
+ for (i--; i >= 0; i--)
+ free_page((unsigned long)__va(pgd_val(pgd[i])-1));
+ kfree(pgd);
+ return NULL;
+}

- if (ret) {
-#if CONFIG_X86_PAE
- int i;
- for (i = 0; i < USER_PTRS_PER_PGD; i++)
- __pgd_clear(ret + i);
#else
- memset(ret, 0, USER_PTRS_PER_PGD * sizeof(pgd_t));
-#endif
- memcpy(ret + USER_PTRS_PER_PGD, swapper_pg_dir + USER_PTRS_PER_PGD, (PTRS_PER_PGD - USER_PTRS_PER_PGD) * sizeof(pgd_t));
+
+extern __inline__ pgd_t *get_pgd_slow(void)
+{
+ pgd_t *pgd = (pgd_t *)__get_free_page(GFP_KERNEL);
+
+ if (pgd) {
+ memset(pgd, 0, USER_PTRS_PER_PGD * sizeof(pgd_t));
+ memcpy(pgd + USER_PTRS_PER_PGD, swapper_pg_dir + USER_PTRS_PER_PGD, (PTRS_PER_PGD - USER_PTRS_PER_PGD) * sizeof(pgd_t));
}
- return ret;
+ return pgd;
}

+#endif
+
extern __inline__ pgd_t *get_pgd_fast(void)
{
unsigned long *ret;
@@ -64,7 +83,15 @@

extern __inline__ void free_pgd_slow(pgd_t *pgd)
{
+#if CONFIG_X86_PAE
+ int i;
+
+ for (i = 0; i < USER_PTRS_PER_PGD; i++)
+ free_page((unsigned long)__va(pgd_val(pgd[i])-1));
+ kfree(pgd);
+#else
free_page((unsigned long)pgd);
+#endif
}

static inline pte_t *pte_alloc_one(void)
@@ -72,7 +99,8 @@
pte_t *pte;

pte = (pte_t *) __get_free_page(GFP_KERNEL);
- clear_page(pte);
+ if (pte)
+ clear_page(pte);
return pte;
}

@@ -100,7 +128,6 @@
free_page((unsigned long)pte);
}

-#define pte_free_kernel(pte) pte_free_slow(pte)
#define pte_free(pte) pte_free_slow(pte)
#define pgd_free(pgd) free_pgd_slow(pgd)
#define pgd_alloc() get_pgd_fast()
@@ -108,12 +135,15 @@
/*
* allocating and freeing a pmd is trivial: the 1-entry pmd is
* inside the pgd, so has no extra memory associated with it.
- * (In the PAE case we free the page.)
+ * (In the PAE case we free the pmds as part of the pgd.)
*/
-#define pmd_free_one(pmd) free_pmd_slow(pmd)

-#define pmd_free_kernel pmd_free
-#define pmd_alloc_kernel pmd_alloc
+#define pmd_alloc_one_fast() ({ BUG(); ((pmd_t *)1); })
+#define pmd_alloc_one() ({ BUG(); ((pmd_t *)2); })
+#define pmd_free_slow(x) do { } while (0)
+#define pmd_free_fast(x) do { } while (0)
+#define pmd_free(x) do { } while (0)
+#define pgd_populate(pmd, pte) BUG()

extern int do_check_pgt_cache(int, int);

--- linux/include/asm-i386/pgtable.h.orig Sun Mar 25 19:03:58 2001
+++ linux/include/asm-i386/pgtable.h Sun Mar 25 23:34:02 2001
@@ -243,12 +243,6 @@
/* page table for 0-4MB for everybody */
extern unsigned long pg0[1024];

-/*
- * Handling allocation failures during page table setup.
- */
-extern void __handle_bad_pmd(pmd_t * pmd);
-extern void __handle_bad_pmd_kernel(pmd_t * pmd);
-
#define pte_present(x) ((x).pte_low & (_PAGE_PRESENT | _PAGE_PROTNONE))
#define pte_clear(xp) do { set_pte(xp, __pte(0)); } while (0)

--- linux/include/asm-i386/pgalloc-2level.h.orig Sun Mar 25 22:36:30 2001
+++ linux/include/asm-i386/pgalloc-2level.h Sun Mar 25 22:38:47 2001
@@ -1,16 +0,0 @@
-#ifndef _I386_PGALLOC_2LEVEL_H
-#define _I386_PGALLOC_2LEVEL_H
-
-/*
- * traditional i386 two-level paging, page table allocation routines:
- * We don't have any real pmd's, and this code never triggers because
- * the pgd will always be present..
- */
-#define pmd_alloc_one_fast() ({ BUG(); ((pmd_t *)1); })
-#define pmd_alloc_one() ({ BUG(); ((pmd_t *)2); })
-#define pmd_free_slow(x) do { } while (0)
-#define pmd_free_fast(x) do { } while (0)
-#define pmd_free(x) do { } while (0)
-#define pgd_populate(pmd, pte) BUG()
-
-#endif /* _I386_PGALLOC_2LEVEL_H */
--- linux/include/asm-i386/pgtable-3level.h.orig Sun Mar 25 23:22:35 2001
+++ linux/include/asm-i386/pgtable-3level.h Sun Mar 25 23:28:41 2001
@@ -33,17 +33,9 @@
#define pgd_ERROR(e) \
printk("%s:%d: bad pgd %p(%016Lx).\n", __FILE__, __LINE__, &(e), pgd_val(e))

-/*
- * Subtle, in PAE mode we cannot have zeroes in the top level
- * page directory, the CPU enforces this. (ie. the PGD entry
- * always has to have the present bit set.) The CPU caches
- * the 4 pgd entries internally, so there is no extra memory
- * load on TLB miss, despite one more level of indirection.
- */
-#define EMPTY_PGD (__pa(empty_zero_page) + 1)
-#define pgd_none(x) (pgd_val(x) == EMPTY_PGD)
+extern inline int pgd_none(pgd_t pgd) { return 0; }
extern inline int pgd_bad(pgd_t pgd) { return 0; }
-extern inline int pgd_present(pgd_t pgd) { return !pgd_none(pgd); }
+extern inline int pgd_present(pgd_t pgd) { return 1; }

/* Rules for using set_pte: the pte being assigned *must* be
* either not present or in a state where the hardware will
@@ -63,21 +55,12 @@
set_64bit((unsigned long long *)(pgdptr),pgd_val(pgdval))

/*
- * Pentium-II errata A13: in PAE mode we explicitly have to flush
- * the TLB via cr3 if the top-level pgd is changed... This was one tough
- * thing to find out - guess i should first read all the documentation
- * next time around ;)
+ * Pentium-II erratum A13: in PAE mode we explicitly have to flush
+ * the TLB via cr3 if the top-level pgd is changed...
+ * We do not let the generic code free and clear pgd entries due to
+ * this erratum.
*/
-extern inline void __pgd_clear (pgd_t * pgd)
-{
- set_pgd(pgd, __pgd(EMPTY_PGD));
-}
-
-extern inline void pgd_clear (pgd_t * pgd)
-{
- __pgd_clear(pgd);
- __flush_tlb();
-}
+extern inline void pgd_clear (pgd_t * pgd) { }

#define pgd_page(pgd) \
((unsigned long) __va(pgd_val(pgd) & PAGE_MASK))
--- linux/arch/i386/mm/init.c.orig Sun Mar 25 19:02:05 2001
+++ linux/arch/i386/mm/init.c Sun Mar 25 23:33:37 2001
@@ -40,77 +40,6 @@
static unsigned long totalram_pages;
static unsigned long totalhigh_pages;

-/*
- * BAD_PAGE is the page that is used for page faults when linux
- * is out-of-memory. Older versions of linux just did a
- * do_exit(), but using this instead means there is less risk
- * for a process dying in kernel mode, possibly leaving an inode
- * unused etc..
- *
- * BAD_PAGETABLE is the accompanying page-table: it is initialized
- * to point to BAD_PAGE entries.
- *
- * ZERO_PAGE is a special page that is used for zero-initialized
- * data and COW.
- */
-
-/*
- * These are allocated in head.S so that we get proper page alignment.
- * If you change the size of these then change head.S as well.
- */
-extern char empty_bad_page[PAGE_SIZE];
-#if CONFIG_X86_PAE
-extern pmd_t empty_bad_pmd_table[PTRS_PER_PMD];
-#endif
-extern pte_t empty_bad_pte_table[PTRS_PER_PTE];
-
-/*
- * We init them before every return and make them writable-shared.
- * This guarantees we get out of the kernel in some more or less sane
- * way.
- */
-#if CONFIG_X86_PAE
-static pmd_t * get_bad_pmd_table(void)
-{
- pmd_t v;
- int i;
-
- set_pmd(&v, __pmd(_PAGE_TABLE + __pa(empty_bad_pte_table)));
-
- for (i = 0; i < PAGE_SIZE/sizeof(pmd_t); i++)
- empty_bad_pmd_table[i] = v;
-
- return empty_bad_pmd_table;
-}
-#endif
-
-static pte_t * get_bad_pte_table(void)
-{
- pte_t v;
- int i;
-
- v = pte_mkdirty(mk_pte_phys(__pa(empty_bad_page), PAGE_SHARED));
-
- for (i = 0; i < PAGE_SIZE/sizeof(pte_t); i++)
- empty_bad_pte_table[i] = v;
-
- return empty_bad_pte_table;
-}
-
-
-
-void __handle_bad_pmd(pmd_t *pmd)
-{
- pmd_ERROR(*pmd);
- set_pmd(pmd, __pmd(_PAGE_TABLE + __pa(get_bad_pte_table())));
-}
-
-void __handle_bad_pmd_kernel(pmd_t *pmd)
-{
- pmd_ERROR(*pmd);
- set_pmd(pmd, __pmd(_KERNPG_TABLE + __pa(get_bad_pte_table())));
-}
-
int do_check_pgt_cache(int low, int high)
{
int freed = 0;
@@ -289,10 +218,8 @@

pgd_base = swapper_pg_dir;
#if CONFIG_X86_PAE
- for (i = 0; i < PTRS_PER_PGD; i++) {
- pgd = pgd_base + i;
- __pgd_clear(pgd);
- }
+ for (i = 0; i < PTRS_PER_PGD; i++)
+ set_pgd(pgd_base + i, __pgd(1 + __pa(empty_zero_page)));
#endif
i = __pgd_offset(PAGE_OFFSET);
pgd = pgd_base + i;
--- linux/arch/i386/kernel/head.S.orig Sun Mar 25 19:04:23 2001
+++ linux/arch/i386/kernel/head.S Sun Mar 25 19:04:57 2001
@@ -415,23 +415,6 @@
ENTRY(empty_zero_page)

.org 0x5000
-ENTRY(empty_bad_page)
-
-.org 0x6000
-ENTRY(empty_bad_pte_table)
-
-#if CONFIG_X86_PAE
-
- .org 0x7000
- ENTRY(empty_bad_pmd_table)
-
- .org 0x8000
-
-#else
-
- .org 0x7000
-
-#endif

/*
* This starts the data section. Note that the above is all
--- linux/MAINTAINERS.orig Sun Mar 25 19:23:13 2001
+++ linux/MAINTAINERS Sun Mar 25 19:24:46 2001
@@ -1454,6 +1454,11 @@
L: linux-x25@vger.kernel.org
S: Maintained

+X86 3-LEVEL PAGING (PAE) SUPPORT
+P: Ingo Molnar
+M: mingo@redhat.com
+S: Maintained
+
Z85230 SYNCHRONOUS DRIVER
P: Alan Cox
M: alan@redhat.com