Re: [PATCH net-next v4 1/4] mm: add a signature in struct page
From: Matthew Wilcox <willy@infradead.org>
Date: 2021-05-12 18:12:23
Also in:
bpf, linux-mm, lkml, netdev
Subsystem:
memory management - core, the rest · Maintainers:
Andrew Morton, David Hildenbrand, Linus Torvalds
On Tue, May 11, 2021 at 05:25:36PM +0300, Ilias Apalodimas wrote:
Nope not at all, either would work. we'll switch to that
You'll need something like this because of the current use of page->index to mean "pfmemalloc". From ecd6d912056a21bbe55d997c01f96b0b8b9fbc31 Mon Sep 17 00:00:00 2001 From: "Matthew Wilcox (Oracle)" <willy@infradead.org> Date: Fri, 16 Apr 2021 18:12:33 -0400 Subject: [PATCH] mm: Indicate pfmemalloc pages in compound_head 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 bd21864449bf..4f9b2007efad 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h@@ -1670,10 +1670,12 @@ struct address_space *page_mapping(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; } /*
@@ -1682,12 +1684,12 @@ 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..1352e278939b 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; + struct page_pool *pp; + unsigned long _pp_mapping_pad; unsigned long dma_addr[2]; }; struct { /* slab, slob and slub */
--
2.30.2