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mm: rename _count, field of the struct page, to _refcount

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Many developers already know that field for reference count of the
struct page is _count and atomic type.  They would try to handle it
directly and this could break the purpose of page reference count
tracepoint.  To prevent direct _count modification, this patch rename it
to _refcount and add warning message on the code.  After that, developer
who need to handle reference count will find that field should not be
accessed directly.

[akpm@linux-foundation.org: fix comments, per Vlastimil]
[akpm@linux-foundation.org: Documentation/vm/transhuge.txt too]
[sfr@canb.auug.org.au: sync ethernet driver changes]
Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Hugh Dickins <hughd@google.com>
Cc: Johannes Berg <johannes@sipsolutions.net>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Sunil Goutham <sgoutham@cavium.com>
Cc: Chris Metcalf <cmetcalf@mellanox.com>
Cc: Manish Chopra <manish.chopra@qlogic.com>
Cc: Yuval Mintz <yuval.mintz@qlogic.com>
Cc: Tariq Toukan <tariqt@mellanox.com>
Cc: Saeed Mahameed <saeedm@mellanox.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Joonsoo Kim 2016-05-19 17:10:49 -07:00 • committed by Linus Torvalds
parent 6d061f9f61
commit 0139aa7b7f
17 changed files with 58 additions and 54 deletions
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8
include/linux/pagemap.h
View file

@ -90,12 +90,12 @@ void release_pages(struct page **pages, int nr, bool cold);
/*
* speculatively take a reference to a page.
* If the page is free (_count == 0), then _count is untouched, and 0
* is returned. Otherwise, _count is incremented by 1 and 1 is returned.
* If the page is free (_refcount == 0), then _refcount is untouched, and 0
* is returned. Otherwise, _refcount is incremented by 1 and 1 is returned.
*
* This function must be called inside the same rcu_read_lock() section as has
* been used to lookup the page in the pagecache radix-tree (or page table):
* this allows allocators to use a synchronize_rcu() to stabilize _count.
* this allows allocators to use a synchronize_rcu() to stabilize _refcount.
*
* Unless an RCU grace period has passed, the count of all pages coming out
* of the allocator must be considered unstable. page_count may return higher
@ -111,7 +111,7 @@ void release_pages(struct page **pages, int nr, bool cold);
* 2. conditionally increment refcount
* 3. check the page is still in pagecache (if no, goto 1)
*
* Remove-side that cares about stability of _count (eg. reclaim) has the
* Remove-side that cares about stability of _refcount (eg. reclaim) has the
* following (with tree_lock held for write):
* A. atomically check refcount is correct and set it to 0 (atomic_cmpxchg)
* B. remove page from pagecache