mlock.c

最新最稳定的Linux内存管理模块源代码

/*
 *	linux/mm/mlock.c
 *
 *  (C) Copyright 1995 Linus Torvalds
 *  (C) Copyright 2002 Christoph Hellwig
 */

#include <linux/capability.h>
#include <linux/mman.h>
#include <linux/mm.h>
#include <linux/swap.h>
#include <linux/swapops.h>
#include <linux/pagemap.h>
#include <linux/mempolicy.h>
#include <linux/syscalls.h>
#include <linux/sched.h>
#include <linux/module.h>
#include <linux/rmap.h>
#include <linux/mmzone.h>
#include <linux/hugetlb.h>

#include "internal.h"

int can_do_mlock(void)
{
	if (capable(CAP_IPC_LOCK))
		return 1;
	if (current->signal->rlim[RLIMIT_MEMLOCK].rlim_cur != 0)
		return 1;
	return 0;
}
EXPORT_SYMBOL(can_do_mlock);

#ifdef CONFIG_UNEVICTABLE_LRU
/*
 * Mlocked pages are marked with PageMlocked() flag for efficient testing
 * in vmscan and, possibly, the fault path; and to support semi-accurate
 * statistics.
 *
 * An mlocked page [PageMlocked(page)] is unevictable.  As such, it will
 * be placed on the LRU "unevictable" list, rather than the [in]active lists.
 * The unevictable list is an LRU sibling list to the [in]active lists.
 * PageUnevictable is set to indicate the unevictable state.
 *
 * When lazy mlocking via vmscan, it is important to ensure that the
 * vma's VM_LOCKED status is not concurrently being modified, otherwise we
 * may have mlocked a page that is being munlocked. So lazy mlock must take
 * the mmap_sem for read, and verify that the vma really is locked
 * (see mm/rmap.c).
 */

/*
 *  LRU accounting for clear_page_mlock()
 */
void __clear_page_mlock(struct page *page)
{
	VM_BUG_ON(!PageLocked(page));

	if (!page->mapping) {	/* truncated ? */
		return;
	}

	dec_zone_page_state(page, NR_MLOCK);
	count_vm_event(UNEVICTABLE_PGCLEARED);
	if (!isolate_lru_page(page)) {
		putback_lru_page(page);
	} else {
		/*
		 * We lost the race. the page already moved to evictable list.
		 */
		if (PageUnevictable(page))
			count_vm_event(UNEVICTABLE_PGSTRANDED);
	}
}

/*
 * Mark page as mlocked if not already.
 * If page on LRU, isolate and putback to move to unevictable list.
 */
void mlock_vma_page(struct page *page)
{
	BUG_ON(!PageLocked(page));

	if (!TestSetPageMlocked(page)) {
		inc_zone_page_state(page, NR_MLOCK);
		count_vm_event(UNEVICTABLE_PGMLOCKED);
		if (!isolate_lru_page(page))
			putback_lru_page(page);
	}
}

/*
 * called from munlock()/munmap() path with page supposedly on the LRU.
 *
 * Note:  unlike mlock_vma_page(), we can't just clear the PageMlocked
 * [in try_to_munlock()] and then attempt to isolate the page.  We must
 * isolate the page to keep others from messing with its unevictable
 * and mlocked state while trying to munlock.  However, we pre-clear the
 * mlocked state anyway as we might lose the isolation race and we might
 * not get another chance to clear PageMlocked.  If we successfully
 * isolate the page and try_to_munlock() detects other VM_LOCKED vmas
 * mapping the page, it will restore the PageMlocked state, unless the page
 * is mapped in a non-linear vma.  So, we go ahead and SetPageMlocked(),
 * perhaps redundantly.
 * If we lose the isolation race, and the page is mapped by other VM_LOCKED
 * vmas, we'll detect this in vmscan--via try_to_munlock() or try_to_unmap()
 * either of which will restore the PageMlocked state by calling
 * mlock_vma_page() above, if it can grab the vma's mmap sem.
 */
static void munlock_vma_page(struct page *page)
{
	BUG_ON(!PageLocked(page));

	if (TestClearPageMlocked(page)) {
		dec_zone_page_state(page, NR_MLOCK);
		if (!isolate_lru_page(page)) {
			int ret = try_to_munlock(page);
			/*
			 * did try_to_unlock() succeed or punt?
			 */
			if (ret == SWAP_SUCCESS || ret == SWAP_AGAIN)
				count_vm_event(UNEVICTABLE_PGMUNLOCKED);

			putback_lru_page(page);
		} else {
			/*
			 * We lost the race.  let try_to_unmap() deal
			 * with it.  At least we get the page state and
			 * mlock stats right.  However, page is still on
			 * the noreclaim list.  We'll fix that up when
			 * the page is eventually freed or we scan the
			 * noreclaim list.
			 */
			if (PageUnevictable(page))
				count_vm_event(UNEVICTABLE_PGSTRANDED);
			else
				count_vm_event(UNEVICTABLE_PGMUNLOCKED);
		}
	}
}

/**
 * __mlock_vma_pages_range() -  mlock/munlock a range of pages in the vma.
 * @vma:   target vma
 * @start: start address
 * @end:   end address
 * @mlock: 0 indicate munlock, otherwise mlock.
 *
 * If @mlock == 0, unlock an mlocked range;
 * else mlock the range of pages.  This takes care of making the pages present ,
 * too.
 *
 * return 0 on success, negative error code on error.
 *
 * vma->vm_mm->mmap_sem must be held for at least read.
 */
static long __mlock_vma_pages_range(struct vm_area_struct *vma,
				   unsigned long start, unsigned long end,
				   int mlock)
{
	struct mm_struct *mm = vma->vm_mm;
	unsigned long addr = start;
	struct page *pages[16]; /* 16 gives a reasonable batch */
	int nr_pages = (end - start) / PAGE_SIZE;
	int ret = 0;
	int gup_flags = 0;

	VM_BUG_ON(start & ~PAGE_MASK);
	VM_BUG_ON(end   & ~PAGE_MASK);
	VM_BUG_ON(start < vma->vm_start);
	VM_BUG_ON(end   > vma->vm_end);
	VM_BUG_ON((!rwsem_is_locked(&mm->mmap_sem)) &&
		  (atomic_read(&mm->mm_users) != 0));

	/*
	 * mlock:   don't page populate if vma has PROT_NONE permission.
	 * munlock: always do munlock although the vma has PROT_NONE
	 *          permission, or SIGKILL is pending.
	 */
	if (!mlock)
		gup_flags |= GUP_FLAGS_IGNORE_VMA_PERMISSIONS |
			     GUP_FLAGS_IGNORE_SIGKILL;

	if (vma->vm_flags & VM_WRITE)
		gup_flags |= GUP_FLAGS_WRITE;

	while (nr_pages > 0) {
		int i;

		cond_resched();

		/*
		 * get_user_pages makes pages present if we are
		 * setting mlock. and this extra reference count will
		 * disable migration of this page.  However, page may
		 * still be truncated out from under us.
		 */
		ret = __get_user_pages(current, mm, addr,
				min_t(int, nr_pages, ARRAY_SIZE(pages)),
				gup_flags, pages, NULL);
		/*
		 * This can happen for, e.g., VM_NONLINEAR regions before
		 * a page has been allocated and mapped at a given offset,
		 * or for addresses that map beyond end of a file.
		 * We'll mlock the the pages if/when they get faulted in.
		 */
		if (ret < 0)
			break;
		if (ret == 0) {
			/*
			 * We know the vma is there, so the only time
			 * we cannot get a single page should be an
			 * error (ret < 0) case.
			 */
			WARN_ON(1);
			break;
		}

		lru_add_drain();	/* push cached pages to LRU */

		for (i = 0; i < ret; i++) {
			struct page *page = pages[i];

			lock_page(page);
			/*
			 * Because we lock page here and migration is blocked
			 * by the elevated reference, we need only check for
			 * page truncation (file-cache only).
			 */
			if (page->mapping) {
				if (mlock)
					mlock_vma_page(page);
				else
					munlock_vma_page(page);
			}
			unlock_page(page);
			put_page(page);		/* ref from get_user_pages() */

			/*
			 * here we assume that get_user_pages() has given us
			 * a list of virtually contiguous pages.
			 */
			addr += PAGE_SIZE;	/* for next get_user_pages() */
			nr_pages--;
		}
		ret = 0;
	}

	return ret;	/* count entire vma as locked_vm */
}

/*
 * convert get_user_pages() return value to posix mlock() error
 */
static int __mlock_posix_error_return(long retval)
{
	if (retval == -EFAULT)
		retval = -ENOMEM;
	else if (retval == -ENOMEM)
		retval = -EAGAIN;
	return retval;
}

#else /* CONFIG_UNEVICTABLE_LRU */

/*
 * Just make pages present if VM_LOCKED.  No-op if unlocking.
 */
static long __mlock_vma_pages_range(struct vm_area_struct *vma,
				   unsigned long start, unsigned long end,
				   int mlock)
{
	if (mlock && (vma->vm_flags & VM_LOCKED))
		return make_pages_present(start, end);
	return 0;
}

static inline int __mlock_posix_error_return(long retval)
{
	return 0;
}

#endif /* CONFIG_UNEVICTABLE_LRU */

/**
 * mlock_vma_pages_range() - mlock pages in specified vma range.
 * @vma - the vma containing the specfied address range
 * @start - starting address in @vma to mlock
 * @end   - end address [+1] in @vma to mlock
 *
 * For mmap()/mremap()/expansion of mlocked vma.
 *
 * return 0 on success for "normal" vmas.
 *
 * return number of pages [> 0] to be removed from locked_vm on success
 * of "special" vmas.
 */
long mlock_vma_pages_range(struct vm_area_struct *vma,
			unsigned long start, unsigned long end)
{
	int nr_pages = (end - start) / PAGE_SIZE;
	BUG_ON(!(vma->vm_flags & VM_LOCKED));

	/*
	 * filter unlockable vmas
	 */
	if (vma->vm_flags & (VM_IO | VM_PFNMAP))
		goto no_mlock;

	if (!((vma->vm_flags & (VM_DONTEXPAND | VM_RESERVED)) ||
			is_vm_hugetlb_page(vma) ||
			vma == get_gate_vma(current))) {

		__mlock_vma_pages_range(vma, start, end, 1);

		/* Hide errors from mmap() and other callers */
		return 0;
	}

	/*
	 * User mapped kernel pages or huge pages:
	 * make these pages present to populate the ptes, but
	 * fall thru' to reset VM_LOCKED--no need to unlock, and
	 * return nr_pages so these don't get counted against task's
	 * locked limit.  huge pages are already counted against
	 * locked vm limit.
	 */
	make_pages_present(start, end);

no_mlock:
	vma->vm_flags &= ~VM_LOCKED;	/* and don't come back! */
	return nr_pages;		/* error or pages NOT mlocked */
}


/*
 * munlock_vma_pages_range() - munlock all pages in the vma range.'
 * @vma - vma containing range to be munlock()ed.
 * @start - start address in @vma of the range
 * @end - end of range in @vma.
 *