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-rw-r--r--include/linux/mm.h68
-rw-r--r--include/linux/page-flags.h35
-rw-r--r--mm/filemap.c8
3 files changed, 64 insertions, 47 deletions
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 2db4229a0066..f2018775b995 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -219,7 +219,8 @@ struct inode;
219 * Each physical page in the system has a struct page associated with 219 * Each physical page in the system has a struct page associated with
220 * it to keep track of whatever it is we are using the page for at the 220 * it to keep track of whatever it is we are using the page for at the
221 * moment. Note that we have no way to track which tasks are using 221 * moment. Note that we have no way to track which tasks are using
222 * a page. 222 * a page, though if it is a pagecache page, rmap structures can tell us
223 * who is mapping it.
223 */ 224 */
224struct page { 225struct page {
225 unsigned long flags; /* Atomic flags, some possibly 226 unsigned long flags; /* Atomic flags, some possibly
@@ -299,8 +300,7 @@ struct page {
299 */ 300 */
300 301
301/* 302/*
302 * Drop a ref, return true if the logical refcount fell to zero (the page has 303 * Drop a ref, return true if the refcount fell to zero (the page has no users)
303 * no users)
304 */ 304 */
305static inline int put_page_testzero(struct page *page) 305static inline int put_page_testzero(struct page *page)
306{ 306{
@@ -356,43 +356,55 @@ void split_page(struct page *page, unsigned int order);
356 * For the non-reserved pages, page_count(page) denotes a reference count. 356 * For the non-reserved pages, page_count(page) denotes a reference count.
357 * page_count() == 0 means the page is free. page->lru is then used for 357 * page_count() == 0 means the page is free. page->lru is then used for
358 * freelist management in the buddy allocator. 358 * freelist management in the buddy allocator.
359 * page_count() == 1 means the page is used for exactly one purpose 359 * page_count() > 0 means the page has been allocated.
360 * (e.g. a private data page of one process).
361 * 360 *
362 * A page may be used for kmalloc() or anyone else who does a 361 * Pages are allocated by the slab allocator in order to provide memory
363 * __get_free_page(). In this case the page_count() is at least 1, and 362 * to kmalloc and kmem_cache_alloc. In this case, the management of the
364 * all other fields are unused but should be 0 or NULL. The 363 * page, and the fields in 'struct page' are the responsibility of mm/slab.c
365 * management of this page is the responsibility of the one who uses 364 * unless a particular usage is carefully commented. (the responsibility of
366 * it. 365 * freeing the kmalloc memory is the caller's, of course).
367 * 366 *
368 * The other pages (we may call them "process pages") are completely 367 * A page may be used by anyone else who does a __get_free_page().
368 * In this case, page_count still tracks the references, and should only
369 * be used through the normal accessor functions. The top bits of page->flags
370 * and page->virtual store page management information, but all other fields
371 * are unused and could be used privately, carefully. The management of this
372 * page is the responsibility of the one who allocated it, and those who have
373 * subsequently been given references to it.
374 *
375 * The other pages (we may call them "pagecache pages") are completely
369 * managed by the Linux memory manager: I/O, buffers, swapping etc. 376 * managed by the Linux memory manager: I/O, buffers, swapping etc.
370 * The following discussion applies only to them. 377 * The following discussion applies only to them.
371 * 378 *
372 * A page may belong to an inode's memory mapping. In this case, 379 * A pagecache page contains an opaque `private' member, which belongs to the
373 * page->mapping is the pointer to the inode, and page->index is the 380 * page's address_space. Usually, this is the address of a circular list of
374 * file offset of the page, in units of PAGE_CACHE_SIZE. 381 * the page's disk buffers. PG_private must be set to tell the VM to call
382 * into the filesystem to release these pages.
375 * 383 *
376 * A page contains an opaque `private' member, which belongs to the 384 * A page may belong to an inode's memory mapping. In this case, page->mapping
377 * page's address_space. Usually, this is the address of a circular 385 * is the pointer to the inode, and page->index is the file offset of the page,
378 * list of the page's disk buffers. 386 * in units of PAGE_CACHE_SIZE.
379 * 387 *
380 * For pages belonging to inodes, the page_count() is the number of 388 * If pagecache pages are not associated with an inode, they are said to be
381 * attaches, plus 1 if `private' contains something, plus one for 389 * anonymous pages. These may become associated with the swapcache, and in that
382 * the page cache itself. 390 * case PG_swapcache is set, and page->private is an offset into the swapcache.
383 * 391 *
384 * Instead of keeping dirty/clean pages in per address-space lists, we instead 392 * In either case (swapcache or inode backed), the pagecache itself holds one
385 * now tag pages as dirty/under writeback in the radix tree. 393 * reference to the page. Setting PG_private should also increment the
394 * refcount. The each user mapping also has a reference to the page.
386 * 395 *
387 * There is also a per-mapping radix tree mapping index to the page 396 * The pagecache pages are stored in a per-mapping radix tree, which is
388 * in memory if present. The tree is rooted at mapping->root. 397 * rooted at mapping->page_tree, and indexed by offset.
398 * Where 2.4 and early 2.6 kernels kept dirty/clean pages in per-address_space
399 * lists, we instead now tag pages as dirty/writeback in the radix tree.
389 * 400 *
390 * All process pages can do I/O: 401 * All pagecache pages may be subject to I/O:
391 * - inode pages may need to be read from disk, 402 * - inode pages may need to be read from disk,
392 * - inode pages which have been modified and are MAP_SHARED may need 403 * - inode pages which have been modified and are MAP_SHARED may need
393 * to be written to disk, 404 * to be written back to the inode on disk,
394 * - private pages which have been modified may need to be swapped out 405 * - anonymous pages (including MAP_PRIVATE file mappings) which have been
395 * to swap space and (later) to be read back into memory. 406 * modified may need to be swapped out to swap space and (later) to be read
407 * back into memory.
396 */ 408 */
397 409
398/* 410/*
diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index 5748642e9f36..9d7921dd50f0 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -13,24 +13,25 @@
13 * PG_reserved is set for special pages, which can never be swapped out. Some 13 * PG_reserved is set for special pages, which can never be swapped out. Some
14 * of them might not even exist (eg empty_bad_page)... 14 * of them might not even exist (eg empty_bad_page)...
15 * 15 *
16 * The PG_private bitflag is set if page->private contains a valid value. 16 * The PG_private bitflag is set on pagecache pages if they contain filesystem
17 * specific data (which is normally at page->private). It can be used by
18 * private allocations for its own usage.
17 * 19 *
18 * During disk I/O, PG_locked is used. This bit is set before I/O and 20 * During initiation of disk I/O, PG_locked is set. This bit is set before I/O
19 * reset when I/O completes. page_waitqueue(page) is a wait queue of all tasks 21 * and cleared when writeback _starts_ or when read _completes_. PG_writeback
20 * waiting for the I/O on this page to complete. 22 * is set before writeback starts and cleared when it finishes.
23 *
24 * PG_locked also pins a page in pagecache, and blocks truncation of the file
25 * while it is held.
26 *
27 * page_waitqueue(page) is a wait queue of all tasks waiting for the page
28 * to become unlocked.
21 * 29 *
22 * PG_uptodate tells whether the page's contents is valid. When a read 30 * PG_uptodate tells whether the page's contents is valid. When a read
23 * completes, the page becomes uptodate, unless a disk I/O error happened. 31 * completes, the page becomes uptodate, unless a disk I/O error happened.
24 * 32 *
25 * For choosing which pages to swap out, inode pages carry a PG_referenced bit, 33 * PG_referenced, PG_reclaim are used for page reclaim for anonymous and
26 * which is set any time the system accesses that page through the (mapping, 34 * file-backed pagecache (see mm/vmscan.c).
27 * index) hash table. This referenced bit, together with the referenced bit
28 * in the page tables, is used to manipulate page->age and move the page across
29 * the active, inactive_dirty and inactive_clean lists.
30 *
31 * Note that the referenced bit, the page->lru list_head and the active,
32 * inactive_dirty and inactive_clean lists are protected by the
33 * zone->lru_lock, and *NOT* by the usual PG_locked bit!
34 * 35 *
35 * PG_error is set to indicate that an I/O error occurred on this page. 36 * PG_error is set to indicate that an I/O error occurred on this page.
36 * 37 *
@@ -42,6 +43,10 @@
42 * space, they need to be kmapped separately for doing IO on the pages. The 43 * space, they need to be kmapped separately for doing IO on the pages. The
43 * struct page (these bits with information) are always mapped into kernel 44 * struct page (these bits with information) are always mapped into kernel
44 * address space... 45 * address space...
46 *
47 * PG_buddy is set to indicate that the page is free and in the buddy system
48 * (see mm/page_alloc.c).
49 *
45 */ 50 */
46 51
47/* 52/*
@@ -74,7 +79,7 @@
74#define PG_checked 8 /* kill me in 2.5.<early>. */ 79#define PG_checked 8 /* kill me in 2.5.<early>. */
75#define PG_arch_1 9 80#define PG_arch_1 9
76#define PG_reserved 10 81#define PG_reserved 10
77#define PG_private 11 /* Has something at ->private */ 82#define PG_private 11 /* If pagecache, has fs-private data */
78 83
79#define PG_writeback 12 /* Page is under writeback */ 84#define PG_writeback 12 /* Page is under writeback */
80#define PG_nosave 13 /* Used for system suspend/resume */ 85#define PG_nosave 13 /* Used for system suspend/resume */
@@ -83,7 +88,7 @@
83 88
84#define PG_mappedtodisk 16 /* Has blocks allocated on-disk */ 89#define PG_mappedtodisk 16 /* Has blocks allocated on-disk */
85#define PG_reclaim 17 /* To be reclaimed asap */ 90#define PG_reclaim 17 /* To be reclaimed asap */
86#define PG_nosave_free 18 /* Free, should not be written */ 91#define PG_nosave_free 18 /* Used for system suspend/resume */
87#define PG_buddy 19 /* Page is free, on buddy lists */ 92#define PG_buddy 19 /* Page is free, on buddy lists */
88 93
89 94
diff --git a/mm/filemap.c b/mm/filemap.c
index d5af1cab4268..afcdc72b5e90 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -599,8 +599,8 @@ void fastcall __lock_page_nosync(struct page *page)
599 * @mapping: the address_space to search 599 * @mapping: the address_space to search
600 * @offset: the page index 600 * @offset: the page index
601 * 601 *
602 * A rather lightweight function, finding and getting a reference to a 602 * Is there a pagecache struct page at the given (mapping, offset) tuple?
603 * hashed page atomically. 603 * If yes, increment its refcount and return it; if no, return NULL.
604 */ 604 */
605struct page * find_get_page(struct address_space *mapping, unsigned long offset) 605struct page * find_get_page(struct address_space *mapping, unsigned long offset)
606{ 606{
@@ -987,7 +987,7 @@ page_not_up_to_date:
987 /* Get exclusive access to the page ... */ 987 /* Get exclusive access to the page ... */
988 lock_page(page); 988 lock_page(page);
989 989
990 /* Did it get unhashed before we got the lock? */ 990 /* Did it get truncated before we got the lock? */
991 if (!page->mapping) { 991 if (!page->mapping) {
992 unlock_page(page); 992 unlock_page(page);
993 page_cache_release(page); 993 page_cache_release(page);
@@ -1627,7 +1627,7 @@ no_cached_page:
1627page_not_uptodate: 1627page_not_uptodate:
1628 lock_page(page); 1628 lock_page(page);
1629 1629
1630 /* Did it get unhashed while we waited for it? */ 1630 /* Did it get truncated while we waited for it? */
1631 if (!page->mapping) { 1631 if (!page->mapping) {
1632 unlock_page(page); 1632 unlock_page(page);
1633 goto err; 1633 goto err;