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Message-Id: <20160329122313.3c24964faab99f46c960b19b@linux-foundation.org>
Date: Tue, 29 Mar 2016 12:23:13 -0700
From: Andrew Morton <akpm@...ux-foundation.org>
To: Vlastimil Babka <vbabka@...e.cz>
Cc: js1304@...il.com, Hugh Dickins <hughd@...gle.com>,
Johannes Berg <johannes@...solutions.net>,
"David S. Miller" <davem@...emloft.net>,
Sunil Goutham <sgoutham@...ium.com>,
Chris Metcalf <cmetcalf@...lanox.com>, linux-mm@...ck.org,
linux-kernel@...r.kernel.org, Joonsoo Kim <iamjoonsoo.kim@....com>
Subject: Re: [PATCH v2 2/2] mm: rename _count, field of the struct page, to
_refcount
On Tue, 29 Mar 2016 11:27:47 +0200 Vlastimil Babka <vbabka@...e.cz> wrote:
> > v2: change more _count usages to _refcount
>
> There's also
> Documentation/vm/transhuge.txt talking about ->_count
> include/linux/mm.h: * requires to already have an elevated page->_count.
> include/linux/mm_types.h: * Keep _count separate from slub cmpxchg_double data.
> include/linux/mm_types.h: * slab_lock but _count is not.
> include/linux/pagemap.h: * If the page is free (_count == 0), then _count is untouched, and 0
> include/linux/pagemap.h: * is returned. Otherwise, _count is incremented by 1 and 1 is returned.
> include/linux/pagemap.h: * this allows allocators to use a synchronize_rcu() to stabilize _count.
> include/linux/pagemap.h: * Remove-side that cares about stability of _count (eg. reclaim) has the
> mm/huge_memory.c: * tail_page->_count is zero and not changing from under us. But
> mm/huge_memory.c: /* Prevent deferred_split_scan() touching ->_count */
> mm/internal.h: * Turn a non-refcounted page (->_count == 0) into refcounted with
> mm/page_alloc.c: bad_reason = "nonzero _count";
> mm/page_alloc.c: bad_reason = "nonzero _count";
> mm/page_alloc.c: * because their page->_count is zero at all time.
> mm/slub.c: * as page->_count. If we assign to ->counters directly
> mm/slub.c: * we run the risk of losing updates to page->_count, so
> mm/vmscan.c: * load is not satisfied before that of page->_count.
> mm/vmscan.c: * The downside is that we have to touch page->_count against each page.
>
> I've arrived at the following command to find this:
> git grep "[^a-zA-Z0-9_]_count[^_]"
>
> Not that many false positives in the output :)
From: Andrew Morton <akpm@...ux-foundation.org>
Subject: mm-rename-_count-field-of-the-struct-page-to-_refcount-fix
fix comments, per Vlastimil
Cc: Vlastimil Babka <vbabka@...e.cz>
Cc: "David S. Miller" <davem@...emloft.net>
Cc: Chris Metcalf <cmetcalf@...lanox.com>
Cc: Hugh Dickins <hughd@...gle.com>
Cc: Johannes Berg <johannes@...solutions.net>
Cc: Joonsoo Kim <iamjoonsoo.kim@....com>
Cc: Sunil Goutham <sgoutham@...ium.com>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
---
drivers/block/aoe/aoecmd.c | 2 +-
drivers/hwtracing/intel_th/msu.c | 2 +-
fs/proc/page.c | 2 +-
include/linux/mm.h | 2 +-
include/linux/mm_types.h | 6 +++---
include/linux/pagemap.h | 8 ++++----
mm/huge_memory.c | 4 ++--
mm/internal.h | 2 +-
mm/page_alloc.c | 2 +-
mm/slub.c | 4 ++--
mm/vmscan.c | 4 ++--
11 files changed, 19 insertions(+), 19 deletions(-)
diff -puN drivers/block/aoe/aoecmd.c~mm-rename-_count-field-of-the-struct-page-to-_refcount-fix drivers/block/aoe/aoecmd.c
--- a/drivers/block/aoe/aoecmd.c~mm-rename-_count-field-of-the-struct-page-to-_refcount-fix
+++ a/drivers/block/aoe/aoecmd.c
@@ -861,7 +861,7 @@ rqbiocnt(struct request *r)
* discussion.
*
* We cannot use get_page in the workaround, because it insists on a
- * positive page count as a precondition. So we use _count directly.
+ * positive page count as a precondition. So we use _refcount directly.
*/
static void
bio_pageinc(struct bio *bio)
diff -puN drivers/hwtracing/intel_th/msu.c~mm-rename-_count-field-of-the-struct-page-to-_refcount-fix drivers/hwtracing/intel_th/msu.c
--- a/drivers/hwtracing/intel_th/msu.c~mm-rename-_count-field-of-the-struct-page-to-_refcount-fix
+++ a/drivers/hwtracing/intel_th/msu.c
@@ -1164,7 +1164,7 @@ static void msc_mmap_close(struct vm_are
if (!atomic_dec_and_mutex_lock(&msc->mmap_count, &msc->buf_mutex))
return;
- /* drop page _counts */
+ /* drop page _refcounts */
for (pg = 0; pg < msc->nr_pages; pg++) {
struct page *page = msc_buffer_get_page(msc, pg);
diff -puN fs/proc/page.c~mm-rename-_count-field-of-the-struct-page-to-_refcount-fix fs/proc/page.c
--- a/fs/proc/page.c~mm-rename-_count-field-of-the-struct-page-to-_refcount-fix
+++ a/fs/proc/page.c
@@ -142,7 +142,7 @@ u64 stable_page_flags(struct page *page)
/*
- * Caveats on high order pages: page->_count will only be set
+ * Caveats on high order pages: page->_refcount will only be set
* -1 on the head page; SLUB/SLQB do the same for PG_slab;
* SLOB won't set PG_slab at all on compound pages.
*/
diff -puN include/linux/mm.h~mm-rename-_count-field-of-the-struct-page-to-_refcount-fix include/linux/mm.h
--- a/include/linux/mm.h~mm-rename-_count-field-of-the-struct-page-to-_refcount-fix
+++ a/include/linux/mm.h
@@ -721,7 +721,7 @@ static inline void get_page(struct page
page = compound_head(page);
/*
* Getting a normal page or the head of a compound page
- * requires to already have an elevated page->_count.
+ * requires to already have an elevated page->_refcount.
*/
VM_BUG_ON_PAGE(page_ref_count(page) <= 0, page);
page_ref_inc(page);
diff -puN include/linux/mm_types.h~mm-rename-_count-field-of-the-struct-page-to-_refcount-fix include/linux/mm_types.h
--- a/include/linux/mm_types.h~mm-rename-_count-field-of-the-struct-page-to-_refcount-fix
+++ a/include/linux/mm_types.h
@@ -73,9 +73,9 @@ struct page {
unsigned long counters;
#else
/*
- * Keep _count separate from slub cmpxchg_double data.
- * As the rest of the double word is protected by
- * slab_lock but _count is not.
+ * Keep _refcount separate from slub cmpxchg_double
+ * data. As the rest of the double word is protected by
+ * slab_lock but _refcount is not.
*/
unsigned counters;
#endif
diff -puN include/linux/pagemap.h~mm-rename-_count-field-of-the-struct-page-to-_refcount-fix include/linux/pagemap.h
--- a/include/linux/pagemap.h~mm-rename-_count-field-of-the-struct-page-to-_refcount-fix
+++ a/include/linux/pagemap.h
@@ -105,12 +105,12 @@ void release_pages(struct page **pages,
/*
* 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
@@ -126,7 +126,7 @@ void release_pages(struct page **pages,
* 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
diff -puN mm/huge_memory.c~mm-rename-_count-field-of-the-struct-page-to-_refcount-fix mm/huge_memory.c
--- a/mm/huge_memory.c~mm-rename-_count-field-of-the-struct-page-to-_refcount-fix
+++ a/mm/huge_memory.c
@@ -3120,7 +3120,7 @@ static void __split_huge_page_tail(struc
VM_BUG_ON_PAGE(page_ref_count(page_tail) != 0, page_tail);
/*
- * tail_page->_count is zero and not changing from under us. But
+ * tail_page->_refcount is zero and not changing from under us. But
* get_page_unless_zero() may be running from under us on the
* tail_page. If we used atomic_set() below instead of atomic_inc(), we
* would then run atomic_set() concurrently with
@@ -3289,7 +3289,7 @@ int split_huge_page_to_list(struct page
if (mlocked)
lru_add_drain();
- /* Prevent deferred_split_scan() touching ->_count */
+ /* Prevent deferred_split_scan() touching ->_refcount */
spin_lock_irqsave(&pgdata->split_queue_lock, flags);
count = page_count(head);
mapcount = total_mapcount(head);
diff -puN mm/internal.h~mm-rename-_count-field-of-the-struct-page-to-_refcount-fix mm/internal.h
--- a/mm/internal.h~mm-rename-_count-field-of-the-struct-page-to-_refcount-fix
+++ a/mm/internal.h
@@ -58,7 +58,7 @@ static inline unsigned long ra_submit(st
}
/*
- * Turn a non-refcounted page (->_count == 0) into refcounted with
+ * Turn a non-refcounted page (->_refcount == 0) into refcounted with
* a count of one.
*/
static inline void set_page_refcounted(struct page *page)
diff -puN mm/page_alloc.c~mm-rename-_count-field-of-the-struct-page-to-_refcount-fix mm/page_alloc.c
--- a/mm/page_alloc.c~mm-rename-_count-field-of-the-struct-page-to-_refcount-fix
+++ a/mm/page_alloc.c
@@ -6864,7 +6864,7 @@ bool has_unmovable_pages(struct zone *zo
* We can't use page_count without pin a page
* because another CPU can free compound page.
* This check already skips compound tails of THP
- * because their page->_count is zero at all time.
+ * because their page->_refcount is zero at all time.
*/
if (!page_ref_count(page)) {
if (PageBuddy(page))
diff -puN mm/slub.c~mm-rename-_count-field-of-the-struct-page-to-_refcount-fix mm/slub.c
--- a/mm/slub.c~mm-rename-_count-field-of-the-struct-page-to-_refcount-fix
+++ a/mm/slub.c
@@ -329,8 +329,8 @@ static inline void set_page_slub_counter
tmp.counters = counters_new;
/*
* page->counters can cover frozen/inuse/objects as well
- * as page->_count. If we assign to ->counters directly
- * we run the risk of losing updates to page->_count, so
+ * as page->_refcount. If we assign to ->counters directly
+ * we run the risk of losing updates to page->_refcount, so
* be careful and only assign to the fields we need.
*/
page->frozen = tmp.frozen;
diff -puN mm/vmscan.c~mm-rename-_count-field-of-the-struct-page-to-_refcount-fix mm/vmscan.c
--- a/mm/vmscan.c~mm-rename-_count-field-of-the-struct-page-to-_refcount-fix
+++ a/mm/vmscan.c
@@ -633,7 +633,7 @@ static int __remove_mapping(struct addre
*
* Reversing the order of the tests ensures such a situation cannot
* escape unnoticed. The smp_rmb is needed to ensure the page->flags
- * load is not satisfied before that of page->_count.
+ * load is not satisfied before that of page->_refcount.
*
* Note that if SetPageDirty is always performed via set_page_dirty,
* and thus under tree_lock, then this ordering is not required.
@@ -1720,7 +1720,7 @@ shrink_inactive_list(unsigned long nr_to
* It is safe to rely on PG_active against the non-LRU pages in here because
* nobody will play with that bit on a non-LRU page.
*
- * The downside is that we have to touch page->_count against each page.
+ * The downside is that we have to touch page->_refcount against each page.
* But we had to alter page->flags anyway.
*/
_
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