On 5/13/23 15:21, David Hildenbrand wrote:
Yes, makes sense.
[1] Total is 1 Gbyte, and running
| dd if=/dev/zero bs=896M count=1 | pv --rate-limit=1k >/dev/null
might not be the best style but does the trick: Wait for pv to
count up to a minute, then ^C it. If the host is still okay after
that, it's considered "good".
Thanks for bisecting and coming up with a testcase!
The attached patch survives for me on my C3000 with 2GB RAM with this test:
dd if=/dev/zero bs=1896M count=1 | pv
(well, the OOM-killer might jump in, but even that is survived).
Could you try the patch below?
Thanks for debugging! :)
[PATCH] parisc: Fix encoding of swp_entry due to added SWP_EXCLUSIVE flag
Fix the __swp_offset() and __swp_entry() macros due to commit 6d239fc78c0b
("parisc/mm: support __HAVE_ARCH_PTE_SWP_EXCLUSIVE") which introduced the
SWP_EXCLUSIVE flag by reusing the _PAGE_ACCESSED flag.
Reported-by: Christoph Biedl <linux-kernel.bfrz@xxxxxxxxxxxxxxxxxx>
Fixes: 6d239fc78c0b ("parisc/mm: support __HAVE_ARCH_PTE_SWP_EXCLUSIVE")
diff --git a/arch/parisc/include/asm/pgtable.h b/arch/parisc/include/asm/pgtable.h
index e2950f5db7c9..522846be54b7 100644
--- a/arch/parisc/include/asm/pgtable.h
+++ b/arch/parisc/include/asm/pgtable.h
@@ -413,12 +413,12 @@ extern void paging_init (void);
* For the 64bit version, the offset is extended by 32bit.
*/
#define __swp_type(x) ((x).val & 0x1f)
-#define __swp_offset(x) ( (((x).val >> 6) & 0x7) | \
- (((x).val >> 8) & ~0x7) )
+#define __swp_offset(x) ( (((x).val >> 5) & 0x7) | \
+ (((x).val >> 10) << 3) )
#define __swp_entry(type, offset) ((swp_entry_t) { \
((type) & 0x1f) | \
- ((offset & 0x7) << 6) | \
- ((offset & ~0x7) << 8) })
+ ((offset & 0x7) << 5) | \
+ ((offset & ~0x7) << 7) })
#define __pte_to_swp_entry(pte) ((swp_entry_t) { pte_val(pte) })
#define __swp_entry_to_pte(x) ((pte_t) { (x).val })
This fix makes it work like the layout I documented.
Yes, and your layout looks good for me.
What I originally tried doing was reusing one of the spare bits instead of reworking
the layout. Apparently, I got the old layout wrong. :(
Don't worry! Your patch harmonizes parisc to the other platforms, which is good.
So if I understood the layout right this time, maybe we can just use one of the two
spare bits: _PAGE_HUGE (or alternatively, _PAGE_DIRTY_BIT)?
Yes, or keep what you suggested.
What I don't understand yet is the original code:
#define __swp_type(x) ((x).val & 0x1f)
#define __swp_offset(x) ( (((x).val >> 6) & 0x7) | \
(((x).val >> 8) & ~0x7) )
#define __swp_entry(type, offset) ((swp_entry_t) { (type) | \
((offset & 0x7) << 6) | \
((offset & ~0x7) << 8) })
Don't we loose one of the offset bits?
Mask 0x7 is 3 bits, but we shift by 6 and 8 (=2 bits difference), so I believe the second shift should be 9.
If it would be 9, then no &0x07 is needed and only one shift would be sufficient.
I don't know much in the swap pte area, but isn't the previous original code wrong?
Which bits of the swp_entry are used where?
Helge
diff --git a/arch/parisc/include/asm/pgtable.h b/arch/parisc/include/asm/pgtable.h
index e2950f5db7c9..ee9f08cd5938 100644
--- a/arch/parisc/include/asm/pgtable.h
+++ b/arch/parisc/include/asm/pgtable.h
@@ -218,8 +218,8 @@ extern void __update_cache(pte_t pte);
#define _PAGE_KERNEL_RWX (_PAGE_KERNEL_EXEC | _PAGE_WRITE)
#define _PAGE_KERNEL (_PAGE_KERNEL_RO | _PAGE_WRITE)
-/* We borrow bit 23 to store the exclusive marker in swap PTEs. */
-#define _PAGE_SWP_EXCLUSIVE _PAGE_ACCESSED
+/* We borrow bit 21 to store the exclusive marker in swap PTEs. */
+#define _PAGE_SWP_EXCLUSIVE _PAGE_HUGE
/* The pgd/pmd contains a ptr (in phys addr space); since all pgds/pmds
* are page-aligned, we don't care about the PAGE_OFFSET bits, except
@@ -405,7 +405,7 @@ extern void paging_init (void);
*
* 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3
* 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
- * <---------------- offset -----------------> P E <ofs> < type ->
+ * <---------------- offset ---------------> E P <ofs> 0 < type ->
*
* E is the exclusive marker that is not stored in swap entries.
* _PAGE_PRESENT (P) must be 0.
diff --git a/lib/maple_tree.c b/lib/maple_tree.c
index 110a36479dce..7510db355f48 100644
