include/linux/page-flags.h

Source file repositories/reference/linux-study-clean/include/linux/page-flags.h

File Facts

System
Linux kernel
Corpus path
include/linux/page-flags.h
Extension
.h
Size
40844 bytes
Lines
1233
Domain
Core OS
Bucket
Core Kernel Interface
Inferred role
Core OS: implementation source
Status
source implementation candidate

Why This File Exists

Core operating-system implementation surface: boot, tasks, memory, VFS, syscall-facing interfaces, synchronization, credentials, and isolation.

Dependency Surface

Detected Declarations

Annotated Snippet

#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. The "struct page" of such a page
 * should in general not be touched (e.g. set dirty) except by its owner.
 * Pages marked as PG_reserved include:
 * - Pages part of the kernel image (including vDSO) and similar (e.g. BIOS,
 *   initrd, HW tables)
 * - Pages reserved or allocated early during boot (before the page allocator
 *   was initialized). This includes (depending on the architecture) the
 *   initial vmemmap, initial page tables, crashkernel, elfcorehdr, and much
 *   much more. Once (if ever) freed, PG_reserved is cleared and they will
 *   be given to the page allocator.
 * - Pages falling into physical memory gaps - not IORESOURCE_SYSRAM. Trying
 *   to read/write these pages might end badly. Don't touch!
 * - The zero page(s)
 * - Pages allocated in the context of kexec/kdump (loaded kernel image,
 *   control pages, vmcoreinfo)
 * - MMIO/DMA pages. Some architectures don't allow to ioremap pages that are
 *   not marked PG_reserved (as they might be in use by somebody else who does
 *   not respect the caching strategy).
 * - MCA pages on ia64
 * - Pages holding CPU notes for POWER Firmware Assisted Dump
 * - Device memory (e.g. PMEM, DAX, HMM)
 * Some PG_reserved pages will be excluded from the hibernation image.
 * PG_reserved does in general not hinder anybody from dumping or swapping
 * and is no longer required for remap_pfn_range(). ioremap might require it.
 * Consequently, PG_reserved for a page mapped into user space can indicate
 * the zero page, the vDSO, MMIO pages or device memory.
 *
 * 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_swapbacked is set when a page uses swap as a backing storage.  This are
 * usually PageAnon or shmem pages but please note that even anonymous pages
 * might lose their PG_swapbacked flag when they simply can be dropped (e.g. as
 * a result of MADV_FREE).
 *
 * PG_referenced, PG_reclaim are used for page reclaim for anonymous and
 * file-backed pagecache (see mm/vmscan.c).
 *
 * 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_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 pageflags directly.  Use the PageFoo macros.
 *
 * 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_writeback,		/* Page is under writeback */

Annotation

Implementation Notes