Hoi Peter,
On Fri, Feb 7, 2020 at 12:34 PM Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
On Fri, Feb 07, 2020 at 11:56:40AM +0100, Geert Uytterhoeven wrote:
On Fri, Jan 31, 2020 at 1:56 PM Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
In addition to the PGD/PMD table size (128*4) add a PTE table size
(64*4) to the table allocator. This completely removes the pte-table
overhead compared to the old code, even for dense tables.
Thanks for your patch!
Notes:
- the allocator gained a list_empty() check to deal with there not
being any pages at all.
- the free mask is extended to cover more than the 8 bits required
for the (512 byte) PGD/PMD tables.
Being an mm-illiterate, I don't understand the relation between the number
of bits and the size (see below).
If the table translates 7 bits of the address, it will have 1<<7 entries.
- NR_PAGETABLE accounting is restored.
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
WARNING: Missing Signed-off-by: line by nominal patch author 'Peter
Zijlstra <peterz@xxxxxxxxxxxxx>'
(in all patches)
I can fix that (the From?) up while applying.
I'm not sure where that warning comes from, but if you feel it needs
fixing, sure. I normally only add the (Intel) thing to the SoB. I've so
far never had complaints about that.
Checkpatch doesn't like this.
--- a/arch/m68k/mm/motorola.c
+++ b/arch/m68k/mm/motorola.c
@@ -72,24 +72,35 @@ void mmu_page_dtor(void *page)
arch/sparc/mm/srmmu.c ... */
typedef struct list_head ptable_desc;
-static LIST_HEAD(ptable_list);
+
+static struct list_head ptable_list[2] = {
+ LIST_HEAD_INIT(ptable_list[0]),
+ LIST_HEAD_INIT(ptable_list[1]),
+};
#define PD_PTABLE(page) ((ptable_desc *)&(virt_to_page(page)->lru))
#define PD_PAGE(ptable) (list_entry(ptable, struct page, lru))
-#define PD_MARKBITS(dp) (*(unsigned char *)&PD_PAGE(dp)->index)
+#define PD_MARKBITS(dp) (*(unsigned int *)&PD_PAGE(dp)->index)
+
+static const int ptable_shift[2] = {
+ 7+2, /* PGD, PMD */
+ 6+2, /* PTE */
+};
-#define PTABLE_SIZE (PTRS_PER_PMD * sizeof(pmd_t))
+#define ptable_size(type) (1U << ptable_shift[type])
+#define ptable_mask(type) ((1U << (PAGE_SIZE / ptable_size(type))) - 1)
So this is 0xff for PGD and PMD, like before, and 0xffff for PTE.
Why the latter value?
The PGD/PMD being 7 bits are sizeof(unsigned long) << 7, or 512 bytes
big. In one 4k page, there fit 8 such entries. 0xFF is 8 bits set, one
for each of the 8 512 byte fragments.
For the PTE tables, which are 6 bit and of sizeof(unsigned long) << 6,
or 256 bytes, we can fit 16 in one 4k page, resulting in 0xFFFF.
Thanks!
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx
In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds
