page-flags.h

Go to the documentation of this file.

/*
 * Macros for manipulating and testing page->flags
 */

#ifndef PAGE_FLAGS_H
#define PAGE_FLAGS_H

#include <linux/types.h>
#include <linux/bug.h>
#include <linux/mmdebug.h>
#ifndef __GENERATING_BOUNDS_H
#include <linux/mm_types.h>
#include <generated/bounds.h>
#endif /* !__GENERATING_BOUNDS_H */

/*
 * Various page->flags bits:
 *
 * PG_reserved is set for special pages, which can never be swapped out. Some
 * of them might not even exist (eg empty_bad_page)...
 *
 * The PG_private bitflag is set on pagecache pages if they contain filesystem
 * specific data (which is normally at page->private). It can be used by
 * private allocations for its own usage.
 *
 * During initiation of disk I/O, PG_locked is set. This bit is set before I/O
 * and cleared when writeback _starts_ or when read _completes_. PG_writeback
 * is set before writeback starts and cleared when it finishes.
 *
 * PG_locked also pins a page in pagecache, and blocks truncation of the file
 * while it is held.
 *
 * page_waitqueue(page) is a wait queue of all tasks waiting for the page
 * to become unlocked.
 *
 * PG_uptodate tells whether the page's contents is valid.  When a read
 * completes, the page becomes uptodate, unless a disk I/O error happened.
 *
 * PG_referenced, PG_reclaim are used for page reclaim for anonymous and
 * file-backed pagecache (see mm/vmscan.c).
 *
 * PG_error is set to indicate that an I/O error occurred on this page.
 *
 * PG_arch_1 is an architecture specific page state bit.  The generic code
 * guarantees that this bit is cleared for a page when it first is entered into
 * the page cache.
 *
 * PG_highmem pages are not permanently mapped into the kernel virtual address
 * space, they need to be kmapped separately for doing IO on the pages.  The
 * struct page (these bits with information) are always mapped into kernel
 * address space...
 *
 * PG_hwpoison indicates that a page got corrupted in hardware and contains
 * data with incorrect ECC bits that triggered a machine check. Accessing is
 * not safe since it may cause another machine check. Don't touch!
 */

/*
 * Don't use the *_dontuse flags.  Use the macros.  Otherwise you'll break
 * locked- and dirty-page accounting.
 *
 * The page flags field is split into two parts, the main flags area
 * which extends from the low bits upwards, and the fields area which
 * extends from the high bits downwards.
 *
 *  | FIELD | ... | FLAGS |
 *  N-1           ^       0
 *               (NR_PAGEFLAGS)
 *
 * The fields area is reserved for fields mapping zone, node (for NUMA) and
 * SPARSEMEM section (for variants of SPARSEMEM that require section ids like
 * SPARSEMEM_EXTREME with !SPARSEMEM_VMEMMAP).
 */
enum pageflags {
    PG_locked,      /* Page is locked. Don't touch. */
    PG_error,
    PG_referenced,
    PG_uptodate,
    PG_dirty,
    PG_lru,
    PG_active,
    PG_slab,
    PG_owner_priv_1,    /* Owner use. If pagecache, fs may use*/
    PG_arch_1,
    PG_reserved,
    PG_private,     /* If pagecache, has fs-private data */
    PG_private_2,       /* If pagecache, has fs aux data */
    PG_writeback,       /* Page is under writeback */
#ifdef CONFIG_PAGEFLAGS_EXTENDED
    PG_head,        /* A head page */
    PG_tail,        /* A tail page */
#else
    PG_compound,        /* A compound page */
#endif
    PG_swapcache,       /* Swap page: swp_entry_t in private */
    PG_mappedtodisk,    /* Has blocks allocated on-disk */
    PG_reclaim,     /* To be reclaimed asap */
    PG_swapbacked,      /* Page is backed by RAM/swap */
    PG_unevictable,     /* Page is "unevictable"  */
#ifdef CONFIG_MMU
    PG_mlocked,     /* Page is vma mlocked */
#endif
#ifdef CONFIG_ARCH_USES_PG_UNCACHED
    PG_uncached,        /* Page has been mapped as uncached */
#endif
#ifdef CONFIG_MEMORY_FAILURE
    PG_hwpoison,        /* hardware poisoned page. Don't touch */
#endif
#ifdef CONFIG_TRANSPARENT_HUGEPAGE
    PG_compound_lock,
#endif
    __NR_PAGEFLAGS,

    /* Filesystems */
    PG_checked = PG_owner_priv_1,

    /* Two page bits are conscripted by FS-Cache to maintain local caching
     * state.  These bits are set on pages belonging to the netfs's inodes
     * when those inodes are being locally cached.
     */
    PG_fscache = PG_private_2,  /* page backed by cache */

    /* XEN */
    PG_pinned = PG_owner_priv_1,
    PG_savepinned = PG_dirty,

    /* SLOB */
    PG_slob_free = PG_private,
};

#ifndef __GENERATING_BOUNDS_H

/*
 * Macros to create function definitions for page flags
 */
#define TESTPAGEFLAG(uname, lname)                  \
static inline int Page##uname(const struct page *page)          \
            { return test_bit(PG_##lname, &page->flags); }

#define SETPAGEFLAG(uname, lname)                   \
static inline void SetPage##uname(struct page *page)            \
            { set_bit(PG_##lname, &page->flags); }

#define CLEARPAGEFLAG(uname, lname)                 \
static inline void ClearPage##uname(struct page *page)          \
            { clear_bit(PG_##lname, &page->flags); }

#define __SETPAGEFLAG(uname, lname)                 \
static inline void __SetPage##uname(struct page *page)          \
            { __set_bit(PG_##lname, &page->flags); }

#define __CLEARPAGEFLAG(uname, lname)                   \
static inline void __ClearPage##uname(struct page *page)        \
            { __clear_bit(PG_##lname, &page->flags); }

#define TESTSETFLAG(uname, lname)                   \
static inline int TestSetPage##uname(struct page *page)         \
        { return test_and_set_bit(PG_##lname, &page->flags); }

#define TESTCLEARFLAG(uname, lname)                 \
static inline int TestClearPage##uname(struct page *page)       \
        { return test_and_clear_bit(PG_##lname, &page->flags); }

#define __TESTCLEARFLAG(uname, lname)                   \
static inline int __TestClearPage##uname(struct page *page)     \
        { return __test_and_clear_bit(PG_##lname, &page->flags); }

#define PAGEFLAG(uname, lname) TESTPAGEFLAG(uname, lname)       \
    SETPAGEFLAG(uname, lname) CLEARPAGEFLAG(uname, lname)

#define __PAGEFLAG(uname, lname) TESTPAGEFLAG(uname, lname)     \
    __SETPAGEFLAG(uname, lname)  __CLEARPAGEFLAG(uname, lname)

#define PAGEFLAG_FALSE(uname)                       \
static inline int Page##uname(const struct page *page)          \
            { return 0; }

#define TESTSCFLAG(uname, lname)                    \
    TESTSETFLAG(uname, lname) TESTCLEARFLAG(uname, lname)

#define SETPAGEFLAG_NOOP(uname)                     \
static inline void SetPage##uname(struct page *page) {  }

#define CLEARPAGEFLAG_NOOP(uname)                   \
static inline void ClearPage##uname(struct page *page) {  }

#define __CLEARPAGEFLAG_NOOP(uname)                 \
static inline void __ClearPage##uname(struct page *page) {  }

#define TESTCLEARFLAG_FALSE(uname)                  \
static inline int TestClearPage##uname(struct page *page) { return 0; }

#define __TESTCLEARFLAG_FALSE(uname)                    \
static inline int __TestClearPage##uname(struct page *page) { return 0; }

struct page;    /* forward declaration */

TESTPAGEFLAG(Locked, locked)
PAGEFLAG(Error, error) TESTCLEARFLAG(Error, error)
PAGEFLAG(Referenced, referenced) TESTCLEARFLAG(Referenced, referenced)
PAGEFLAG(Dirty, dirty) TESTSCFLAG(Dirty, dirty) __CLEARPAGEFLAG(Dirty, dirty)
PAGEFLAG(LRU, lru) __CLEARPAGEFLAG(LRU, lru)
PAGEFLAG(Active, active) __CLEARPAGEFLAG(Active, active)
    TESTCLEARFLAG(Active, active)
__PAGEFLAG(Slab, slab)
PAGEFLAG(Checked, checked)      /* Used by some filesystems */
PAGEFLAG(Pinned, pinned) TESTSCFLAG(Pinned, pinned) /* Xen */
PAGEFLAG(SavePinned, savepinned);           /* Xen */
PAGEFLAG(Reserved, reserved) __CLEARPAGEFLAG(Reserved, reserved)
PAGEFLAG(SwapBacked, swapbacked) __CLEARPAGEFLAG(SwapBacked, swapbacked)

__PAGEFLAG(SlobFree, slob_free)

/*
 * Private page markings that may be used by the filesystem that owns the page
 * for its own purposes.
 * - PG_private and PG_private_2 cause releasepage() and co to be invoked
 */
PAGEFLAG(Private, private) __SETPAGEFLAG(Private, private)
    __CLEARPAGEFLAG(Private, private)
PAGEFLAG(Private2, private_2) TESTSCFLAG(Private2, private_2)
PAGEFLAG(OwnerPriv1, owner_priv_1) TESTCLEARFLAG(OwnerPriv1, owner_priv_1)

/*
 * Only test-and-set exist for PG_writeback.  The unconditional operators are
 * risky: they bypass page accounting.
 */
TESTPAGEFLAG(Writeback, writeback) TESTSCFLAG(Writeback, writeback)
PAGEFLAG(MappedToDisk, mappedtodisk)

/* PG_readahead is only used for file reads; PG_reclaim is only for writes */
PAGEFLAG(Reclaim, reclaim) TESTCLEARFLAG(Reclaim, reclaim)
PAGEFLAG(Readahead, reclaim)        /* Reminder to do async read-ahead */

#ifdef CONFIG_HIGHMEM
/*
 * Must use a macro here due to header dependency issues. page_zone() is not
 * available at this point.
 */
#define PageHighMem(__p) is_highmem(page_zone(__p))
#else
PAGEFLAG_FALSE(HighMem)
#endif

#ifdef CONFIG_SWAP
PAGEFLAG(SwapCache, swapcache)
#else
PAGEFLAG_FALSE(SwapCache)
    SETPAGEFLAG_NOOP(SwapCache) CLEARPAGEFLAG_NOOP(SwapCache)
#endif

PAGEFLAG(Unevictable, unevictable) __CLEARPAGEFLAG(Unevictable, unevictable)
    TESTCLEARFLAG(Unevictable, unevictable)

#ifdef CONFIG_MMU
PAGEFLAG(Mlocked, mlocked) __CLEARPAGEFLAG(Mlocked, mlocked)
    TESTSCFLAG(Mlocked, mlocked) __TESTCLEARFLAG(Mlocked, mlocked)
#else
PAGEFLAG_FALSE(Mlocked) SETPAGEFLAG_NOOP(Mlocked)
    TESTCLEARFLAG_FALSE(Mlocked) __TESTCLEARFLAG_FALSE(Mlocked)
#endif

#ifdef CONFIG_ARCH_USES_PG_UNCACHED
PAGEFLAG(Uncached, uncached)
#else
PAGEFLAG_FALSE(Uncached)
#endif

#ifdef CONFIG_MEMORY_FAILURE
PAGEFLAG(HWPoison, hwpoison)
TESTSCFLAG(HWPoison, hwpoison)
#define __PG_HWPOISON (1UL << PG_hwpoison)
#else
PAGEFLAG_FALSE(HWPoison)
#define __PG_HWPOISON 0
#endif

u64 stable_page_flags(struct page *page);

static inline int PageUptodate(struct page *page)
{
    int ret = test_bit(PG_uptodate, &(page)->flags);

    /*
     * Must ensure that the data we read out of the page is loaded
     * _after_ we've loaded page->flags to check for PageUptodate.
     * We can skip the barrier if the page is not uptodate, because
     * we wouldn't be reading anything from it.
     *
     * See SetPageUptodate() for the other side of the story.
     */
    if (ret)
        smp_rmb();

    return ret;
}

static inline void __SetPageUptodate(struct page *page)
{
    smp_wmb();
    __set_bit(PG_uptodate, &(page)->flags);
}

static inline void SetPageUptodate(struct page *page)
{
#ifdef CONFIG_S390
    if (!test_and_set_bit(PG_uptodate, &page->flags))
        page_set_storage_key(page_to_phys(page), PAGE_DEFAULT_KEY, 0);
#else
    /*
     * Memory barrier must be issued before setting the PG_uptodate bit,
     * so that all previous stores issued in order to bring the page
     * uptodate are actually visible before PageUptodate becomes true.
     *
     * s390 doesn't need an explicit smp_wmb here because the test and
     * set bit already provides full barriers.
     */
    smp_wmb();
    set_bit(PG_uptodate, &(page)->flags);
#endif
}

CLEARPAGEFLAG(Uptodate, uptodate)

extern void cancel_dirty_page(struct page *page, unsigned int account_size);

int test_clear_page_writeback(struct page *page);
int test_set_page_writeback(struct page *page);

static inline void set_page_writeback(struct page *page)
{
    test_set_page_writeback(page);
}

#ifdef CONFIG_PAGEFLAGS_EXTENDED
/*
 * System with lots of page flags available. This allows separate
 * flags for PageHead() and PageTail() checks of compound pages so that bit
 * tests can be used in performance sensitive paths. PageCompound is
 * generally not used in hot code paths.
 */
__PAGEFLAG(Head, head) CLEARPAGEFLAG(Head, head)
__PAGEFLAG(Tail, tail)

static inline int PageCompound(struct page *page)
{
    return page->flags & ((1L << PG_head) | (1L << PG_tail));

}
#ifdef CONFIG_TRANSPARENT_HUGEPAGE
static inline void ClearPageCompound(struct page *page)
{
    BUG_ON(!PageHead(page));
    ClearPageHead(page);
}
#endif
#else
/*
 * Reduce page flag use as much as possible by overlapping
 * compound page flags with the flags used for page cache pages. Possible
 * because PageCompound is always set for compound pages and not for
 * pages on the LRU and/or pagecache.
 */
TESTPAGEFLAG(Compound, compound)
__PAGEFLAG(Head, compound)

/*
 * PG_reclaim is used in combination with PG_compound to mark the
 * head and tail of a compound page. This saves one page flag
 * but makes it impossible to use compound pages for the page cache.
 * The PG_reclaim bit would have to be used for reclaim or readahead
 * if compound pages enter the page cache.
 *
 * PG_compound & PG_reclaim => Tail page
 * PG_compound & ~PG_reclaim    => Head page
 */
#define PG_head_tail_mask ((1L << PG_compound) | (1L << PG_reclaim))

static inline int PageTail(struct page *page)
{
    return ((page->flags & PG_head_tail_mask) == PG_head_tail_mask);
}

static inline void __SetPageTail(struct page *page)
{
    page->flags |= PG_head_tail_mask;
}

static inline void __ClearPageTail(struct page *page)
{
    page->flags &= ~PG_head_tail_mask;
}

#ifdef CONFIG_TRANSPARENT_HUGEPAGE
static inline void ClearPageCompound(struct page *page)
{
    BUG_ON((page->flags & PG_head_tail_mask) != (1 << PG_compound));
    clear_bit(PG_compound, &page->flags);
}
#endif

#endif /* !PAGEFLAGS_EXTENDED */

#ifdef CONFIG_TRANSPARENT_HUGEPAGE
/*
 * PageHuge() only returns true for hugetlbfs pages, but not for
 * normal or transparent huge pages.
 *
 * PageTransHuge() returns true for both transparent huge and
 * hugetlbfs pages, but not normal pages. PageTransHuge() can only be
 * called only in the core VM paths where hugetlbfs pages can't exist.
 */
static inline int PageTransHuge(struct page *page)
{
    VM_BUG_ON(PageTail(page));
    return PageHead(page);
}

/*
 * PageTransCompound returns true for both transparent huge pages
 * and hugetlbfs pages, so it should only be called when it's known
 * that hugetlbfs pages aren't involved.
 */
static inline int PageTransCompound(struct page *page)
{
    return PageCompound(page);
}

/*
 * PageTransTail returns true for both transparent huge pages
 * and hugetlbfs pages, so it should only be called when it's known
 * that hugetlbfs pages aren't involved.
 */
static inline int PageTransTail(struct page *page)
{
    return PageTail(page);
}

#else

static inline int PageTransHuge(struct page *page)
{
    return 0;
}

static inline int PageTransCompound(struct page *page)
{
    return 0;
}

static inline int PageTransTail(struct page *page)
{
    return 0;
}
#endif

/*
 * If network-based swap is enabled, sl*b must keep track of whether pages
 * were allocated from pfmemalloc reserves.
 */
static inline int PageSlabPfmemalloc(struct page *page)
{
    VM_BUG_ON(!PageSlab(page));
    return PageActive(page);
}

static inline void SetPageSlabPfmemalloc(struct page *page)
{
    VM_BUG_ON(!PageSlab(page));
    SetPageActive(page);
}

static inline void __ClearPageSlabPfmemalloc(struct page *page)
{
    VM_BUG_ON(!PageSlab(page));
    __ClearPageActive(page);
}

static inline void ClearPageSlabPfmemalloc(struct page *page)
{
    VM_BUG_ON(!PageSlab(page));
    ClearPageActive(page);
}

#ifdef CONFIG_MMU
#define __PG_MLOCKED        (1 << PG_mlocked)
#else
#define __PG_MLOCKED        0
#endif

#ifdef CONFIG_TRANSPARENT_HUGEPAGE
#define __PG_COMPOUND_LOCK      (1 << PG_compound_lock)
#else
#define __PG_COMPOUND_LOCK      0
#endif

/*
 * Flags checked when a page is freed.  Pages being freed should not have
 * these flags set.  It they are, there is a problem.
 */
#define PAGE_FLAGS_CHECK_AT_FREE \
    (1 << PG_lru     | 1 << PG_locked    | \
     1 << PG_private | 1 << PG_private_2 | \
     1 << PG_writeback | 1 << PG_reserved | \
     1 << PG_slab    | 1 << PG_swapcache | 1 << PG_active | \
     1 << PG_unevictable | __PG_MLOCKED | __PG_HWPOISON | \
     __PG_COMPOUND_LOCK)

/*
 * Flags checked when a page is prepped for return by the page allocator.
 * Pages being prepped should not have any flags set.  It they are set,
 * there has been a kernel bug or struct page corruption.
 */
#define PAGE_FLAGS_CHECK_AT_PREP    ((1 << NR_PAGEFLAGS) - 1)

#define PAGE_FLAGS_PRIVATE              \
    (1 << PG_private | 1 << PG_private_2)

static inline int page_has_private(struct page *page)
{
    return !!(page->flags & PAGE_FLAGS_PRIVATE);
}

#endif /* !__GENERATING_BOUNDS_H */

#endif  /* PAGE_FLAGS_H */