Commit e0da382c authored by Hugh Dickins's avatar Hugh Dickins Committed by Linus Torvalds
Browse files

[PATCH] freepgt: free_pgtables use vma list 



Recent woes with some arches needing their own pgd_addr_end macro; and 4-level
clear_page_range regression since 2.6.10's clear_page_tables; and its
long-standing well-known inefficiency in searching throughout the higher-level
page tables for those few entries to clear and free: all can be blamed on
ignoring the list of vmas when we free page tables.

Replace exit_mmap's clear_page_range of the total user address space by
free_pgtables operating on the mm's vma list; unmap_region use it in the same
way, giving floor and ceiling beyond which it may not free tables.  This
brings lmbench fork/exec/sh numbers back to 2.6.10 (unless preempt is enabled,
in which case latency fixes spoil unmap_vmas throughput).

Beware: the do_mmap_pgoff driver failure case must now use unmap_region
instead of zap_page_range, since a page table might have been allocated, and
can only be freed while it is touched by some vma.

Move free_pgtables from mmap.c to memory.c, where its lower levels are adapted
from the clear_page_range levels.  (Most of free_pgtables' old code was
actually for a non-existent case, prev not properly set up, dating from before
hch gave us split_vma.) Pass mmu_gather** in the public interfaces, since we
might want to add latency lockdrops later; but no attempt to do so yet, going
by vma should itself reduce latency.

But what if is_hugepage_only_range?  Those ia64 and ppc64 cases need careful
examination: put that off until a later patch of the series.

What of x86_64's 32bit vdso page __map_syscall32 maps outside any vma?

And the range to sparc64's flush_tlb_pgtables?  It's less clear to me now that
we need to do more than is done here - every PMD_SIZE ever occupied will be
flushed, do we really have to flush every PGDIR_SIZE ever partially occupied? 
A shame to complicate it unnecessarily.

Special thanks to David Miller for time spent repairing my ceilings.

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 9f6c6fc5

arch/i386/mm/pgtable.c

+1 −1
Original line number Diff line number Diff line
@@ -255,6 +255,6 @@ void pgd_free(pgd_t *pgd) 
	if (PTRS_PER_PMD > 1)

		for (i = 0; i < USER_PTRS_PER_PGD; ++i)

			kmem_cache_free(pmd_cache, (void *)__va(pgd_val(pgd[i])-1));

	/* in the non-PAE case, clear_page_range() clears user pgd entries */

	/* in the non-PAE case, free_pgtables() clears user pgd entries */

	kmem_cache_free(pgd_cache, pgd);

}

arch/ia64/mm/hugetlbpage.c

+2 −35
Original line number Diff line number Diff line
@@ -187,45 +187,12 @@ follow_huge_pmd(struct mm_struct *mm, unsigned long address, pmd_t *pmd, int wri 
}



/*

 * Same as generic free_pgtables(), except constant PGDIR_* and pgd_offset

 * are hugetlb region specific.

 * Do nothing, until we've worked out what to do!  To allow build, we

 * must remove reference to clear_page_range since it no longer exists.

 */

void hugetlb_free_pgtables(struct mmu_gather *tlb, struct vm_area_struct *prev,

	unsigned long start, unsigned long end)

{

	unsigned long first = start & HUGETLB_PGDIR_MASK;

	unsigned long last = end + HUGETLB_PGDIR_SIZE - 1;

	struct mm_struct *mm = tlb->mm;



	if (!prev) {

		prev = mm->mmap;

		if (!prev)

			goto no_mmaps;

		if (prev->vm_end > start) {

			if (last > prev->vm_start)

				last = prev->vm_start;

			goto no_mmaps;

		}

	}

	for (;;) {

		struct vm_area_struct *next = prev->vm_next;



		if (next) {

			if (next->vm_start < start) {

				prev = next;

				continue;

			}

			if (last > next->vm_start)

				last = next->vm_start;

		}

		if (prev->vm_end > first)

			first = prev->vm_end;

		break;

	}

no_mmaps:

	if (last < first)	/* for arches with discontiguous pgd indices */

		return;

	clear_page_range(tlb, first, last);

}



void unmap_hugepage_range(struct vm_area_struct *vma, unsigned long start, unsigned long end)

include/linux/mm.h

+2 −1
Original line number Diff line number Diff line
@@ -592,7 +592,8 @@ int unmap_vmas(struct mmu_gather **tlbp, struct mm_struct *mm, 
		struct vm_area_struct *start_vma, unsigned long start_addr,

		unsigned long end_addr, unsigned long *nr_accounted,

		struct zap_details *);

void clear_page_range(struct mmu_gather *tlb, unsigned long addr, unsigned long end);

void free_pgtables(struct mmu_gather **tlb, struct vm_area_struct *vma,

		unsigned long floor, unsigned long ceiling);

int copy_page_range(struct mm_struct *dst, struct mm_struct *src,

			struct vm_area_struct *vma);

int zeromap_page_range(struct vm_area_struct *vma, unsigned long from,

mm/memory.c

+115 −37
Original line number Diff line number Diff line
@@ -110,87 +110,165 @@ void pmd_clear_bad(pmd_t *pmd) 
 * Note: this doesn't free the actual pages themselves. That

 * has been handled earlier when unmapping all the memory regions.

 */

static inline void clear_pte_range(struct mmu_gather *tlb, pmd_t *pmd,

				unsigned long addr, unsigned long end)

static void free_pte_range(struct mmu_gather *tlb, pmd_t *pmd)

{

	if (!((addr | end) & ~PMD_MASK)) {

		/* Only free fully aligned ranges */

	struct page *page = pmd_page(*pmd);

	pmd_clear(pmd);

	pte_free_tlb(tlb, page);

	dec_page_state(nr_page_table_pages);

	tlb->mm->nr_ptes--;

		pte_free_tlb(tlb, page);

	}

}



static inline void clear_pmd_range(struct mmu_gather *tlb, pud_t *pud,

				unsigned long addr, unsigned long end)

static inline void free_pmd_range(struct mmu_gather *tlb, pud_t *pud,

				unsigned long addr, unsigned long end,

				unsigned long floor, unsigned long ceiling)

{

	pmd_t *pmd;

	unsigned long next;

	pmd_t *empty_pmd = NULL;

	unsigned long start;



	start = addr;

	pmd = pmd_offset(pud, addr);



	/* Only free fully aligned ranges */

	if (!((addr | end) & ~PUD_MASK))

		empty_pmd = pmd;

	do {

		next = pmd_addr_end(addr, end);

		if (pmd_none_or_clear_bad(pmd))

			continue;

		clear_pte_range(tlb, pmd, addr, next);

		free_pte_range(tlb, pmd);

	} while (pmd++, addr = next, addr != end);



	if (empty_pmd) {

		pud_clear(pud);

		pmd_free_tlb(tlb, empty_pmd);

	start &= PUD_MASK;

	if (start < floor)

		return;

	if (ceiling) {

		ceiling &= PUD_MASK;

		if (!ceiling)

			return;

	}

	if (end - 1 > ceiling - 1)

		return;



	pmd = pmd_offset(pud, start);

	pud_clear(pud);

	pmd_free_tlb(tlb, pmd);

}



static inline void clear_pud_range(struct mmu_gather *tlb, pgd_t *pgd,

				unsigned long addr, unsigned long end)

static inline void free_pud_range(struct mmu_gather *tlb, pgd_t *pgd,

				unsigned long addr, unsigned long end,

				unsigned long floor, unsigned long ceiling)

{

	pud_t *pud;

	unsigned long next;

	pud_t *empty_pud = NULL;

	unsigned long start;



	start = addr;

	pud = pud_offset(pgd, addr);



	/* Only free fully aligned ranges */

	if (!((addr | end) & ~PGDIR_MASK))

		empty_pud = pud;

	do {

		next = pud_addr_end(addr, end);

		if (pud_none_or_clear_bad(pud))

			continue;

		clear_pmd_range(tlb, pud, addr, next);

		free_pmd_range(tlb, pud, addr, next, floor, ceiling);

	} while (pud++, addr = next, addr != end);



	if (empty_pud) {

		pgd_clear(pgd);

		pud_free_tlb(tlb, empty_pud);

	start &= PGDIR_MASK;

	if (start < floor)

		return;

	if (ceiling) {

		ceiling &= PGDIR_MASK;

		if (!ceiling)

			return;

	}

	if (end - 1 > ceiling - 1)

		return;



	pud = pud_offset(pgd, start);

	pgd_clear(pgd);

	pud_free_tlb(tlb, pud);

}



/*

 * This function clears user-level page tables of a process.

 * Unlike other pagetable walks, some memory layouts might give end 0.

 * This function frees user-level page tables of a process.

 *

 * Must be called with pagetable lock held.

 */

void clear_page_range(struct mmu_gather *tlb,

				unsigned long addr, unsigned long end)

static inline void free_pgd_range(struct mmu_gather *tlb,

			unsigned long addr, unsigned long end,

			unsigned long floor, unsigned long ceiling)

{

	pgd_t *pgd;

	unsigned long next;

	unsigned long start;



	/*

	 * The next few lines have given us lots of grief...

	 *

	 * Why are we testing PMD* at this top level?  Because often

	 * there will be no work to do at all, and we'd prefer not to

	 * go all the way down to the bottom just to discover that.

	 *

	 * Why all these "- 1"s?  Because 0 represents both the bottom

	 * of the address space and the top of it (using -1 for the

	 * top wouldn't help much: the masks would do the wrong thing).

	 * The rule is that addr 0 and floor 0 refer to the bottom of

	 * the address space, but end 0 and ceiling 0 refer to the top

	 * Comparisons need to use "end - 1" and "ceiling - 1" (though

	 * that end 0 case should be mythical).

	 *

	 * Wherever addr is brought up or ceiling brought down, we must

	 * be careful to reject "the opposite 0" before it confuses the

	 * subsequent tests.  But what about where end is brought down

	 * by PMD_SIZE below? no, end can't go down to 0 there.

	 *

	 * Whereas we round start (addr) and ceiling down, by different

	 * masks at different levels, in order to test whether a table

	 * now has no other vmas using it, so can be freed, we don't

	 * bother to round floor or end up - the tests don't need that.

	 */



	addr &= PMD_MASK;

	if (addr < floor) {

		addr += PMD_SIZE;

		if (!addr)

			return;

	}

	if (ceiling) {

		ceiling &= PMD_MASK;

		if (!ceiling)

			return;

	}

	if (end - 1 > ceiling - 1)

		end -= PMD_SIZE;

	if (addr > end - 1)

		return;



	start = addr;

	pgd = pgd_offset(tlb->mm, addr);

	do {

		next = pgd_addr_end(addr, end);

		if (pgd_none_or_clear_bad(pgd))

			continue;

		clear_pud_range(tlb, pgd, addr, next);

		free_pud_range(tlb, pgd, addr, next, floor, ceiling);

	} while (pgd++, addr = next, addr != end);



	if (!tlb_is_full_mm(tlb))

		flush_tlb_pgtables(tlb->mm, start, end);

}



void free_pgtables(struct mmu_gather **tlb, struct vm_area_struct *vma,

				unsigned long floor, unsigned long ceiling)

{

	while (vma) {

		struct vm_area_struct *next = vma->vm_next;

		unsigned long addr = vma->vm_start;



		/* Optimization: gather nearby vmas into a single call down */

		while (next && next->vm_start <= vma->vm_end + PMD_SIZE) {

			vma = next;

			next = vma->vm_next;

		}

		free_pgd_range(*tlb, addr, vma->vm_end,

				floor, next? next->vm_start: ceiling);

		vma = next;

	}

}



pte_t fastcall * pte_alloc_map(struct mm_struct *mm, pmd_t *pmd, unsigned long address)

mm/mmap.c

+21 −81
Original line number Diff line number Diff line
@@ -29,6 +29,10 @@ 
#include <asm/cacheflush.h>

#include <asm/tlb.h>



static void unmap_region(struct mm_struct *mm,

		struct vm_area_struct *vma, struct vm_area_struct *prev,

		unsigned long start, unsigned long end);



/*

 * WARNING: the debugging will use recursive algorithms so never enable this

 * unless you know what you are doing.
@@ -1129,7 +1133,8 @@ unmap_and_free_vma: 
	fput(file);



	/* Undo any partial mapping done by a device driver. */

	zap_page_range(vma, vma->vm_start, vma->vm_end - vma->vm_start, NULL);

	unmap_region(mm, vma, prev, vma->vm_start, vma->vm_end);

	charged = 0;

free_vma:

	kmem_cache_free(vm_area_cachep, vma);

unacct_error:
@@ -1572,66 +1577,6 @@ find_extend_vma(struct mm_struct * mm, unsigned long addr) 
}

#endif



/*

 * Try to free as many page directory entries as we can,

 * without having to work very hard at actually scanning

 * the page tables themselves.

 *

 * Right now we try to free page tables if we have a nice

 * PGDIR-aligned area that got free'd up. We could be more

 * granular if we want to, but this is fast and simple,

 * and covers the bad cases.

 *

 * "prev", if it exists, points to a vma before the one

 * we just free'd - but there's no telling how much before.

 */

static void free_pgtables(struct mmu_gather *tlb, struct vm_area_struct *prev,

	unsigned long start, unsigned long end)

{

	unsigned long first = start & PGDIR_MASK;

	unsigned long last = end + PGDIR_SIZE - 1;

	struct mm_struct *mm = tlb->mm;



	if (last > MM_VM_SIZE(mm) || last < end)

		last = MM_VM_SIZE(mm);



	if (!prev) {

		prev = mm->mmap;

		if (!prev)

			goto no_mmaps;

		if (prev->vm_end > start) {

			if (last > prev->vm_start)

				last = prev->vm_start;

			goto no_mmaps;

		}

	}

	for (;;) {

		struct vm_area_struct *next = prev->vm_next;



		if (next) {

			if (next->vm_start < start) {

				prev = next;

				continue;

			}

			if (last > next->vm_start)

				last = next->vm_start;

		}

		if (prev->vm_end > first)

			first = prev->vm_end;

		break;

	}

no_mmaps:

	if (last < first)	/* for arches with discontiguous pgd indices */

		return;

	if (first < FIRST_USER_PGD_NR * PGDIR_SIZE)

		first = FIRST_USER_PGD_NR * PGDIR_SIZE;

	/* No point trying to free anything if we're in the same pte page */

	if ((first & PMD_MASK) < (last & PMD_MASK)) {

		clear_page_range(tlb, first, last);

		flush_tlb_pgtables(mm, first, last);

	}

}



/* Normal function to fix up a mapping

 * This function is the default for when an area has no specific

 * function.  This may be used as part of a more specific routine.
@@ -1674,24 +1619,22 @@ static void unmap_vma_list(struct mm_struct *mm, 
 * Called with the page table lock held.

 */

static void unmap_region(struct mm_struct *mm,

	struct vm_area_struct *vma,

	struct vm_area_struct *prev,

	unsigned long start,

	unsigned long end)

		struct vm_area_struct *vma, struct vm_area_struct *prev,

		unsigned long start, unsigned long end)

{

	struct vm_area_struct *next = prev? prev->vm_next: mm->mmap;

	struct mmu_gather *tlb;

	unsigned long nr_accounted = 0;



	lru_add_drain();

	spin_lock(&mm->page_table_lock);

	tlb = tlb_gather_mmu(mm, 0);

	unmap_vmas(&tlb, mm, vma, start, end, &nr_accounted, NULL);

	vm_unacct_memory(nr_accounted);



	if (is_hugepage_only_range(mm, start, end - start))

		hugetlb_free_pgtables(tlb, prev, start, end);

	else

		free_pgtables(tlb, prev, start, end);

	free_pgtables(&tlb, vma, prev? prev->vm_end: 0,

				 next? next->vm_start: 0);

	tlb_finish_mmu(tlb, start, end);

	spin_unlock(&mm->page_table_lock);

}



/*
@@ -1823,9 +1766,7 @@ int do_munmap(struct mm_struct *mm, unsigned long start, size_t len) 
	 * Remove the vma's, and unmap the actual pages

	 */

	detach_vmas_to_be_unmapped(mm, mpnt, prev, end);

	spin_lock(&mm->page_table_lock);

	unmap_region(mm, mpnt, prev, start, end);

	spin_unlock(&mm->page_table_lock);



	/* Fix up all other VM information */

	unmap_vma_list(mm, mpnt);
@@ -1957,25 +1898,21 @@ EXPORT_SYMBOL(do_brk); 
void exit_mmap(struct mm_struct *mm)

{

	struct mmu_gather *tlb;

	struct vm_area_struct *vma;

	struct vm_area_struct *vma = mm->mmap;

	unsigned long nr_accounted = 0;



	lru_add_drain();



	spin_lock(&mm->page_table_lock);



	tlb = tlb_gather_mmu(mm, 1);

	flush_cache_mm(mm);

	/* Use ~0UL here to ensure all VMAs in the mm are unmapped */

	mm->map_count -= unmap_vmas(&tlb, mm, mm->mmap, 0,

					~0UL, &nr_accounted, NULL);

	tlb = tlb_gather_mmu(mm, 1);

	/* Use -1 here to ensure all VMAs in the mm are unmapped */

	mm->map_count -= unmap_vmas(&tlb, mm, vma, 0, -1, &nr_accounted, NULL);

	vm_unacct_memory(nr_accounted);

	BUG_ON(mm->map_count);	/* This is just debugging */

	clear_page_range(tlb, FIRST_USER_PGD_NR * PGDIR_SIZE, MM_VM_SIZE(mm));

	

	free_pgtables(&tlb, vma, 0, 0);

	tlb_finish_mmu(tlb, 0, MM_VM_SIZE(mm));



	vma = mm->mmap;

	mm->mmap = mm->mmap_cache = NULL;

	mm->mm_rb = RB_ROOT;

	set_mm_counter(mm, rss, 0);
@@ -1993,6 +1930,9 @@ void exit_mmap(struct mm_struct *mm) 
		remove_vm_struct(vma);

		vma = next;

	}



	BUG_ON(mm->map_count);	/* This is just debugging */

	BUG_ON(mm->nr_ptes);	/* This is just debugging */

}



/* Insert vm structure into process list sorted by address

CRA Git | Maintained and supported by SUSTech CRA and CCSE