On 1/24/26 10:56, Mike Rapoport wrote:
From: "Mike Rapoport (Microsoft)" <[email protected]>
Reduce 22 declarations of empty_zero_page to 3 and 23 declarations of
ZERO_PAGE() to 4.
Every architecture defines empty_zero_page that way or another, but for the
most of them it is always a page aligned page in BSS and most definitions
of ZERO_PAGE do virt_to_page(empty_zero_page).
Move Linus vetted x86 definition of empty_zero_page and ZERO_PAGE() to the
core MM and drop these definitions in architectures that do not implement
colored zero page (MIPS and s390).
ZERO_PAGE() remains a macro because turning it to a wrapper for a static
inline causes severe pain in header dependencies.
That's just what I wanted to ask after looking at it :)
For the most part the change is mechanical, with these being noteworthy:
* alpha: aliased empty_zero_page with ZERO_PGE that was also used for boot
parameters. Switching to a generic empty_zero_page removes the aliasing
and keeps ZERO_PGE for boot parameters only
* arm64: uses __pa_symbol() in ZERO_PAGE() so that definition of
ZERO_PAGE() is kept intact.
* m68k/parisc/sparc64/um: allocated empty_zero_page from memblock,
although they do not support zero page coloring and having it in BSS
will work fine.
* sh: used empty_zero_page for boot parameters at the very early boot.
Rename the parameters page to boot_params_page and let sh use the generic
empty_zero_page.
* hexagon: had an amusing comment about empty_zero_page
/* A handy thing to have if one has the RAM. Declared in head.S */
that unfortunately had to go :)
Signed-off-by: Mike Rapoport (Microsoft) <[email protected]>
[...]
+#ifndef __HAVE_COLOR_ZERO_PAGE
+extern unsigned long empty_zero_page[PAGE_SIZE / sizeof(unsigned long)];
+#endif
+
+#ifndef ZERO_PAGE
+#define ZERO_PAGE(vaddr) ((void)(vaddr),virt_to_page(empty_zero_page))
Took me a second ...
+#endif
+
#endif /* !__ASSEMBLY__ */
#if !defined(MAX_POSSIBLE_PHYSMEM_BITS) && !defined(CONFIG_64BIT)
diff --git a/mm/mm_init.c b/mm/mm_init.c
index 1a29a719af58..8ea5b76f317f 100644
--- a/mm/mm_init.c
+++ b/mm/mm_init.c
@@ -53,6 +53,15 @@ EXPORT_SYMBOL(mem_map);
void *high_memory;
EXPORT_SYMBOL(high_memory);
+#ifndef __HAVE_COLOR_ZERO_PAGE
+/*
+ * ZERO_PAGE is a global shared page that is always zero: used
+ * for zero-mapped memory areas etc..
+ */
I am not so sure of how much value that comment here is.
... and in particular, why it is not next to ZERO_PAGE in pgtable.h? ;)
+unsigned long empty_zero_page[PAGE_SIZE / sizeof(unsigned long)]
__page_aligned_bss;
Is there a good (or historic) reason why this is not simply
uint8_t empty_zero_page[PAGE_SIZE] __page_aligned_bss;
Almost looks to simple, right? So there must be some problem with it :)
+EXPORT_SYMBOL(empty_zero_page);
+#endif
Nothing else jumped at me, nice cleanup ... if you get sparc to work :P
--
Cheers,
David
