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[PATCH] update some mm/ comments

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Let's try to keep mm/ comments more useful and up to date. This is a start.

Signed-off-by: Nick Piggin <npiggin@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
This commit is contained in:
Nick Piggin
2006-09-25 23:31:35 -07:00
committed by Linus Torvalds
parent e5ac9c5aec
commit da6052f7b3
3 changed files with 64 additions and 47 deletions
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include/linux/page-flags.h
+20 -15
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@@ -13,24 +13,25 @@
* 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 if page->private contains a valid value.
* 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 disk I/O, PG_locked is used. This bit is set before I/O and
* reset when I/O completes. page_waitqueue(page) is a wait queue of all tasks
* waiting for the I/O on this page to complete.
* 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.
*
* For choosing which pages to swap out, inode pages carry a PG_referenced bit,
* which is set any time the system accesses that page through the (mapping,
* index) hash table. This referenced bit, together with the referenced bit
* in the page tables, is used to manipulate page->age and move the page across
* the active, inactive_dirty and inactive_clean lists.
*
* Note that the referenced bit, the page->lru list_head and the active,
* inactive_dirty and inactive_clean lists are protected by the
* zone->lru_lock, and *NOT* by the usual PG_locked bit!
* 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.
*
@@ -42,6 +43,10 @@
* 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_buddy is set to indicate that the page is free and in the buddy system
* (see mm/page_alloc.c).
*
*/
/*
@@ -74,7 +79,7 @@
#define PG_checked 8 /* kill me in 2.5.<early>. */
#define PG_arch_1 9
#define PG_reserved 10
#define PG_private 11 /* Has something at ->private */
#define PG_private 11 /* If pagecache, has fs-private data */
#define PG_writeback 12 /* Page is under writeback */
#define PG_nosave 13 /* Used for system suspend/resume */
@@ -83,7 +88,7 @@
#define PG_mappedtodisk 16 /* Has blocks allocated on-disk */
#define PG_reclaim 17 /* To be reclaimed asap */
#define PG_nosave_free 18 /* Free, should not be written */
#define PG_nosave_free 18 /* Used for system suspend/resume */
#define PG_buddy 19 /* Page is free, on buddy lists */