From: "Matthew Wilcox (Oracle)" <willy@infradead.org>
To: brouer@redhat.com
Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org,
netdev@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
linux-arm-kernel@lists.infradead.org, linux-mips@vger.kernel.org,
ilias.apalodimas@linaro.org, mcroce@linux.microsoft.com,
grygorii.strashko@ti.com, arnd@kernel.org, hch@lst.de,
linux-snps-arc@lists.infradead.org, mhocko@kernel.org,
mgorman@suse.de
Subject: [PATCH 2/2] mm: Indicate pfmemalloc pages in compound_head
Date: Sat, 17 Apr 2021 00:07:24 +0100 [thread overview]
Message-ID: <20210416230724.2519198-3-willy@infradead.org> (raw)
In-Reply-To: <20210416230724.2519198-1-willy@infradead.org>
The net page_pool wants to use a magic value to identify page pool pages.
The best place to put it is in the first word where it can be clearly a
non-pointer value. That means shifting dma_addr up to alias with ->index,
which means we need to find another way to indicate page_is_pfmemalloc().
Since page_pool doesn't want to set its magic value on pages which are
pfmemalloc, we can use bit 1 of compound_head to indicate that the page
came from the memory reserves.
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
---
include/linux/mm.h | 12 +++++++-----
include/linux/mm_types.h | 7 +++----
2 files changed, 10 insertions(+), 9 deletions(-)
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 8ba434287387..44eab3f6d5ae 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1629,10 +1629,12 @@ struct address_space *page_mapping_file(struct page *page);
static inline bool page_is_pfmemalloc(const struct page *page)
{
/*
- * Page index cannot be this large so this must be
- * a pfmemalloc page.
+ * This is not a tail page; compound_head of a head page is unused
+ * at return from the page allocator, and will be overwritten
+ * by callers who do not care whether the page came from the
+ * reserves.
*/
- return page->index == -1UL;
+ return page->compound_head & 2;
}
/*
@@ -1641,12 +1643,12 @@ static inline bool page_is_pfmemalloc(const struct page *page)
*/
static inline void set_page_pfmemalloc(struct page *page)
{
- page->index = -1UL;
+ page->compound_head = 2;
}
static inline void clear_page_pfmemalloc(struct page *page)
{
- page->index = 0;
+ page->compound_head = 0;
}
/*
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 5aacc1c10a45..39f7163dcace 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -96,10 +96,9 @@ struct page {
unsigned long private;
};
struct { /* page_pool used by netstack */
- /**
- * @dma_addr: might require a 64-bit value on
- * 32-bit architectures.
- */
+ unsigned long pp_magic;
+ unsigned long xmi;
+ unsigned long _pp_mapping_pad;
unsigned long dma_addr[2];
};
struct { /* slab, slob and slub */
--
2.30.2
next prev parent reply other threads:[~2021-04-16 23:08 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-16 23:07 [PATCH 0/2] Change struct page layout for page_pool Matthew Wilcox (Oracle)
2021-04-16 23:07 ` [PATCH 1/2] mm: Fix struct page layout on 32-bit systems Matthew Wilcox (Oracle)
2021-04-17 1:08 ` kernel test robot
2021-04-17 2:45 ` Matthew Wilcox
2021-04-17 18:32 ` Ilias Apalodimas
2021-04-17 20:22 ` Matthew Wilcox
2021-04-18 11:21 ` Ilias Apalodimas
2021-04-17 21:18 ` David Laight
2021-04-17 22:45 ` Matthew Wilcox
2021-04-20 2:48 ` Vineet Gupta
2021-04-20 3:10 ` Matthew Wilcox
2021-04-20 7:07 ` Arnd Bergmann
2021-04-20 21:14 ` Vineet Gupta
2021-04-20 21:20 ` Arnd Bergmann
2021-04-21 5:50 ` hch
2021-04-21 8:43 ` David Laight
2021-04-21 8:58 ` Arnd Bergmann
2021-04-20 7:39 ` Geert Uytterhoeven
2021-04-20 8:39 ` David Laight
2021-04-20 11:32 ` Matthew Wilcox
2021-04-17 7:34 ` Jesper Dangaard Brouer
2021-04-20 7:21 ` Rasmus Villemoes
2021-04-16 23:07 ` Matthew Wilcox (Oracle) [this message]
2021-04-17 21:13 ` [PATCH 2/2] mm: Indicate pfmemalloc pages in compound_head David Laight
2021-04-17 21:28 ` Matthew Wilcox
2021-04-20 4:03 ` [PATCH 0/2] Change struct page layout for page_pool Michael Ellerman
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