Commit 7be7a546 authored by Hugh Dickins's avatar Hugh Dickins Committed by Linus Torvalds
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[PATCH] mm: move_page_tables by extents



Speeding up mremap's moving of ptes has never been a priority, but the locking
will get more complicated shortly, and is already too baroque.

Scrap the current one-by-one moving, do an extent at a time: curtailed by end
of src and dst pmds (have to use PMD_SIZE: the way pmd_addr_end gets elided
doesn't match this usage), and by latency considerations.

One nice property of the old method is lost: it never allocated a page table
unless absolutely necessary, so you could free empty page tables by mremapping
to and fro.  Whereas this way, it allocates a dst table wherever there was a
src table.  I keep diving in to reinstate the old behaviour, then come out
preferring not to clutter how it now is.
Signed-off-by: default avatarHugh Dickins <hugh@veritas.com>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent 65500d23
......@@ -22,40 +22,15 @@
#include <asm/cacheflush.h>
#include <asm/tlbflush.h>
static pte_t *get_one_pte_map_nested(struct mm_struct *mm, unsigned long addr)
{
pgd_t *pgd;
pud_t *pud;
pmd_t *pmd;
pte_t *pte = NULL;
pgd = pgd_offset(mm, addr);
if (pgd_none_or_clear_bad(pgd))
goto end;
pud = pud_offset(pgd, addr);
if (pud_none_or_clear_bad(pud))
goto end;
pmd = pmd_offset(pud, addr);
if (pmd_none_or_clear_bad(pmd))
goto end;
pte = pte_offset_map_nested(pmd, addr);
if (pte_none(*pte)) {
pte_unmap_nested(pte);
pte = NULL;
}
end:
return pte;
}
static pte_t *get_one_pte_map(struct mm_struct *mm, unsigned long addr)
static pmd_t *get_old_pmd(struct mm_struct *mm, unsigned long addr)
{
pgd_t *pgd;
pud_t *pud;
pmd_t *pmd;
/*
* We don't need page_table_lock: we have mmap_sem exclusively.
*/
pgd = pgd_offset(mm, addr);
if (pgd_none_or_clear_bad(pgd))
return NULL;
......@@ -68,35 +43,48 @@ static pte_t *get_one_pte_map(struct mm_struct *mm, unsigned long addr)
if (pmd_none_or_clear_bad(pmd))
return NULL;
return pte_offset_map(pmd, addr);
return pmd;
}
static inline pte_t *alloc_one_pte_map(struct mm_struct *mm, unsigned long addr)
static pmd_t *alloc_new_pmd(struct mm_struct *mm, unsigned long addr)
{
pgd_t *pgd;
pud_t *pud;
pmd_t *pmd;
pte_t *pte = NULL;
pmd_t *pmd = NULL;
pte_t *pte;
/*
* We do need page_table_lock: because allocators expect that.
*/
spin_lock(&mm->page_table_lock);
pgd = pgd_offset(mm, addr);
pud = pud_alloc(mm, pgd, addr);
if (!pud)
return NULL;
goto out;
pmd = pmd_alloc(mm, pud, addr);
if (pmd)
pte = pte_alloc_map(mm, pmd, addr);
return pte;
if (!pmd)
goto out;
pte = pte_alloc_map(mm, pmd, addr);
if (!pte) {
pmd = NULL;
goto out;
}
pte_unmap(pte);
out:
spin_unlock(&mm->page_table_lock);
return pmd;
}
static int
move_one_page(struct vm_area_struct *vma, unsigned long old_addr,
struct vm_area_struct *new_vma, unsigned long new_addr)
static void move_ptes(struct vm_area_struct *vma, pmd_t *old_pmd,
unsigned long old_addr, unsigned long old_end,
struct vm_area_struct *new_vma, pmd_t *new_pmd,
unsigned long new_addr)
{
struct address_space *mapping = NULL;
struct mm_struct *mm = vma->vm_mm;
int error = 0;
pte_t *src, *dst;
pte_t *old_pte, *new_pte, pte;
if (vma->vm_file) {
/*
......@@ -111,74 +99,62 @@ move_one_page(struct vm_area_struct *vma, unsigned long old_addr,
new_vma->vm_truncate_count != vma->vm_truncate_count)
new_vma->vm_truncate_count = 0;
}
spin_lock(&mm->page_table_lock);
src = get_one_pte_map_nested(mm, old_addr);
if (src) {
/*
* Look to see whether alloc_one_pte_map needs to perform a
* memory allocation. If it does then we need to drop the
* atomic kmap
*/
dst = get_one_pte_map(mm, new_addr);
if (unlikely(!dst)) {
pte_unmap_nested(src);
if (mapping)
spin_unlock(&mapping->i_mmap_lock);
dst = alloc_one_pte_map(mm, new_addr);
if (mapping && !spin_trylock(&mapping->i_mmap_lock)) {
spin_unlock(&mm->page_table_lock);
spin_lock(&mapping->i_mmap_lock);
spin_lock(&mm->page_table_lock);
}
src = get_one_pte_map_nested(mm, old_addr);
}
/*
* Since alloc_one_pte_map can drop and re-acquire
* page_table_lock, we should re-check the src entry...
*/
if (src) {
if (dst) {
pte_t pte;
pte = ptep_clear_flush(vma, old_addr, src);
/* ZERO_PAGE can be dependant on virtual addr */
pte = move_pte(pte, new_vma->vm_page_prot,
old_addr, new_addr);
set_pte_at(mm, new_addr, dst, pte);
} else
error = -ENOMEM;
pte_unmap_nested(src);
}
if (dst)
pte_unmap(dst);
spin_lock(&mm->page_table_lock);
old_pte = pte_offset_map(old_pmd, old_addr);
new_pte = pte_offset_map_nested(new_pmd, new_addr);
for (; old_addr < old_end; old_pte++, old_addr += PAGE_SIZE,
new_pte++, new_addr += PAGE_SIZE) {
if (pte_none(*old_pte))
continue;
pte = ptep_clear_flush(vma, old_addr, old_pte);
/* ZERO_PAGE can be dependant on virtual addr */
pte = move_pte(pte, new_vma->vm_page_prot, old_addr, new_addr);
set_pte_at(mm, new_addr, new_pte, pte);
}
pte_unmap_nested(new_pte - 1);
pte_unmap(old_pte - 1);
spin_unlock(&mm->page_table_lock);
if (mapping)
spin_unlock(&mapping->i_mmap_lock);
return error;
}
#define LATENCY_LIMIT (64 * PAGE_SIZE)
static unsigned long move_page_tables(struct vm_area_struct *vma,
unsigned long old_addr, struct vm_area_struct *new_vma,
unsigned long new_addr, unsigned long len)
{
unsigned long offset;
unsigned long extent, next, old_end;
pmd_t *old_pmd, *new_pmd;
flush_cache_range(vma, old_addr, old_addr + len);
old_end = old_addr + len;
flush_cache_range(vma, old_addr, old_end);
/*
* This is not the clever way to do this, but we're taking the
* easy way out on the assumption that most remappings will be
* only a few pages.. This also makes error recovery easier.
*/
for (offset = 0; offset < len; offset += PAGE_SIZE) {
if (move_one_page(vma, old_addr + offset,
new_vma, new_addr + offset) < 0)
break;
for (; old_addr < old_end; old_addr += extent, new_addr += extent) {
cond_resched();
next = (old_addr + PMD_SIZE) & PMD_MASK;
if (next - 1 > old_end)
next = old_end;
extent = next - old_addr;
old_pmd = get_old_pmd(vma->vm_mm, old_addr);
if (!old_pmd)
continue;
new_pmd = alloc_new_pmd(vma->vm_mm, new_addr);
if (!new_pmd)
break;
next = (new_addr + PMD_SIZE) & PMD_MASK;
if (extent > next - new_addr)
extent = next - new_addr;
if (extent > LATENCY_LIMIT)
extent = LATENCY_LIMIT;
move_ptes(vma, old_pmd, old_addr, old_addr + extent,
new_vma, new_pmd, new_addr);
}
return offset;
return len + old_addr - old_end; /* how much done */
}
static unsigned long move_vma(struct vm_area_struct *vma,
......
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