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Date: Mon, 15 Mar 2021 02:24:32 +0000
From: Matthew Wilcox <willy@...radead.org>
To: linux-mm@...ck.org
Cc: linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH v4 07/25] mm: Create FolioFlags
On Fri, Mar 05, 2021 at 04:18:43AM +0000, Matthew Wilcox (Oracle) wrote:
> These new functions are the folio analogues of the PageFlags functions.
> If CONFIG_DEBUG_VM_PGFLAGS is enabled, we check the folio is not a tail
> page at every invocation. Note that this will also catch the PagePoisoned
> case as a poisoned page has every bit set, which would include PageTail.
>
> This saves 1740 bytes of text with the distro-derived config that
> I'm testing due to removing a double call to compound_head() in
> PageSwapCache().
This patch is buggy due to using the wrong page->flags for FolioDoubleMapped.
I'm not totally in love with this fix, but it does work without changing
every PAGEFLAG definition.
(also, I needed FolioTransHuge())
commit fe8ca904171345d113f06f381c255a3c4b20074e
Author: Matthew Wilcox (Oracle) <willy@...radead.org>
Date: Sun Mar 14 17:34:48 2021 -0400
fix FolioFlags
diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index 01aa4a71bf14..b7fd4c3733ca 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -212,10 +212,13 @@ static inline void page_init_poison(struct page *page, size_t size)
}
#endif
-static unsigned long *folio_flags(struct folio *folio)
+static unsigned long *folio_flags(struct folio *folio, unsigned n)
{
- VM_BUG_ON_PGFLAGS(PageTail(&folio->page), &folio->page);
- return &folio->page.flags;
+ struct page *page = &folio->page;
+
+ VM_BUG_ON_PGFLAGS(PageTail(page), page);
+ VM_BUG_ON_PGFLAGS(n > 0 && !test_bit(PG_head, &page->flags), page);
+ return &page[n].flags;
}
/*
@@ -262,48 +265,56 @@ static unsigned long *folio_flags(struct folio *folio)
VM_BUG_ON_PGFLAGS(!PageHead(page), page); \
PF_POISONED_CHECK(&page[1]); })
+/* Which page is the flag stored in */
+#define FOLIO_PF_ANY 0
+#define FOLIO_PF_HEAD 0
+#define FOLIO_PF_ONLY_HEAD 0
+#define FOLIO_PF_NO_TAIL 0
+#define FOLIO_PF_NO_COMPOUND 0
+#define FOLIO_PF_SECOND 1
+
/*
* Macros to create function definitions for page flags
*/
#define TESTPAGEFLAG(uname, lname, policy) \
static __always_inline int Folio##uname(struct folio *folio) \
- { return test_bit(PG_##lname, folio_flags(folio)); } \
+ { return test_bit(PG_##lname, folio_flags(folio, FOLIO_##policy)); } \
static __always_inline int Page##uname(struct page *page) \
{ return test_bit(PG_##lname, &policy(page, 0)->flags); }
#define SETPAGEFLAG(uname, lname, policy) \
static __always_inline void SetFolio##uname(struct folio *folio) \
- { set_bit(PG_##lname, folio_flags(folio)); } \
+ { set_bit(PG_##lname, folio_flags(folio, FOLIO_##policy)); } \
static __always_inline void SetPage##uname(struct page *page) \
{ set_bit(PG_##lname, &policy(page, 1)->flags); }
#define CLEARPAGEFLAG(uname, lname, policy) \
static __always_inline void ClearFolio##uname(struct folio *folio) \
- { clear_bit(PG_##lname, folio_flags(folio)); } \
+ { clear_bit(PG_##lname, folio_flags(folio, FOLIO_##policy)); } \
static __always_inline void ClearPage##uname(struct page *page) \
{ clear_bit(PG_##lname, &policy(page, 1)->flags); }
#define __SETPAGEFLAG(uname, lname, policy) \
static __always_inline void __SetFolio##uname(struct folio *folio) \
- { __set_bit(PG_##lname, folio_flags(folio)); } \
+ { __set_bit(PG_##lname, folio_flags(folio, FOLIO_##policy)); } \
static __always_inline void __SetPage##uname(struct page *page) \
{ __set_bit(PG_##lname, &policy(page, 1)->flags); }
#define __CLEARPAGEFLAG(uname, lname, policy) \
static __always_inline void __ClearFolio##uname(struct folio *folio) \
- { __clear_bit(PG_##lname, folio_flags(folio)); } \
+ { __clear_bit(PG_##lname, folio_flags(folio, FOLIO_##policy)); } \
static __always_inline void __ClearPage##uname(struct page *page) \
{ __clear_bit(PG_##lname, &policy(page, 1)->flags); }
#define TESTSETFLAG(uname, lname, policy) \
static __always_inline int TestSetFolio##uname(struct folio *folio) \
- { return test_and_set_bit(PG_##lname, folio_flags(folio)); } \
+ { return test_and_set_bit(PG_##lname, folio_flags(folio, FOLIO_##policy)); } \
static __always_inline int TestSetPage##uname(struct page *page) \
{ return test_and_set_bit(PG_##lname, &policy(page, 1)->flags); }
#define TESTCLEARFLAG(uname, lname, policy) \
static __always_inline int TestClearFolio##uname(struct folio *folio) \
- { return test_and_clear_bit(PG_##lname, folio_flags(folio)); } \
+ { return test_and_clear_bit(PG_##lname, folio_flags(folio, FOLIO_##policy)); } \
static __always_inline int TestClearPage##uname(struct page *page) \
{ return test_and_clear_bit(PG_##lname, &policy(page, 1)->flags); }
@@ -422,7 +433,7 @@ PAGEFLAG_FALSE(HighMem)
static __always_inline bool FolioSwapCache(struct folio *folio)
{
return FolioSwapBacked(folio) &&
- test_bit(PG_swapcache, folio_flags(folio));
+ test_bit(PG_swapcache, folio_flags(folio, 0));
}
@@ -545,7 +556,7 @@ u64 stable_page_flags(struct page *page);
static inline int FolioUptodate(struct folio *folio)
{
- int ret = test_bit(PG_uptodate, folio_flags(folio));
+ int ret = test_bit(PG_uptodate, folio_flags(folio, 0));
/*
* Must ensure that the data we read out of the page is loaded
* _after_ we've loaded page->flags to check for PageUptodate.
@@ -568,7 +579,7 @@ static inline int PageUptodate(struct page *page)
static __always_inline void __SetFolioUptodate(struct folio *folio)
{
smp_wmb();
- __set_bit(PG_uptodate, folio_flags(folio));
+ __set_bit(PG_uptodate, folio_flags(folio, 0));
}
static __always_inline void SetFolioUptodate(struct folio *folio)
@@ -579,7 +590,7 @@ static __always_inline void SetFolioUptodate(struct folio *folio)
* uptodate are actually visible before PageUptodate becomes true.
*/
smp_wmb();
- set_bit(PG_uptodate, folio_flags(folio));
+ set_bit(PG_uptodate, folio_flags(folio, 0));
}
static __always_inline void __SetPageUptodate(struct page *page)
@@ -672,6 +683,11 @@ static inline int PageTransHuge(struct page *page)
return PageHead(page);
}
+static inline bool FolioTransHuge(struct folio *folio)
+{
+ return FolioHead(folio);
+}
+
/*
* PageTransCompound returns true for both transparent huge pages
* and hugetlbfs pages, so it should only be called when it's known
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