1:33 p.m.
Hi Kasuhito,
I am planning on releasing crash-7.2.1 today, so this will have to be deferred
to 7.2.2.
Because of your questions about ppc64, possible backwards-compatibility issues,
or potential future changes to page.flags usage, this permanent change to the
is_page_ptr() function solely for the purposes of SLUB's count_partial() function
makes me nervous.
There is really no compelling reason that count_partial() absolutely *must* use
is_page_ptr(), and so I'm thinking that perhaps you could come up with a less
heavy-handed method for simply testing whether a page.lru entry points to another
vmemmap'd page. Something along the lines of adding this for vmemmap-enabled
kernels:
#define IN_VMEMMAP_RANGE(page) ((page >= VMEMMAP_VADDR) && (page <=
VMEMMAP_END))
and then have count_partial() replace the is_page_ptr() call with another
slub function that does something like this for vmemmap-enabled kernels:
(IN_VMMEMAP_RANGE(next) && accessible(next))
Or instead of accessible(), it could read "next" as a list_head with
RETURN_ON_ERROR,
and verify that next->prev points back to the current list_head.
Non-vmemmap-enabled kernels could still use is_page_ptr().
What do you think of doing something like that?
Dave
----- Original Message -----
Hi,
The "kmem -[sS]" commands can take several minutes to complete with
the following conditions:
* The system has a lot of memory sections with CONFIG_SPARSEMEM.
* The kernel uses SLUB and it has a very long partial slab list.
crash> kmem -s dentry | awk '{print strftime("%T"), $0}'
10:18:34 CACHE NAME OBJSIZE ALLOCATED TOTAL
SLABS SSIZE
10:19:41 ffff88017fc78a00 dentry 192 9038949 10045728
239184 8k
crash> kmem -S dentry | bash -c 'cat >/dev/null ; echo $SECONDS'
334
One of the causes is that is_page_ptr() in count_partial() checks if
a given slub page address is a page struct by searching all memory
sections linearly for the one which includes it.
nr_mem_sections = NR_MEM_SECTIONS();
for (nr = 0; nr < nr_mem_sections ; nr++) {
if ((sec_addr = valid_section_nr(nr))) {
...
With CONFIG_SPARSEMEM{_VMEMMAP}, we can calculate the memory section
which includes a page struct with its page.flags, or its address and
VMEMMAP_VADDR. With this patch doing so, the computation amount can be
significantly reduced in that case.
crash> kmem -s dentry | awk '{print strftime("%T"), $0}'
10:34:55 CACHE NAME OBJSIZE ALLOCATED TOTAL
SLABS SSIZE
10:34:55 ffff88017fc78a00 dentry 192 9038949 10045728
239184 8k
crash> kmem -S dentry | bash -c 'cat >/dev/null ; echo $SECONDS'
2
This patch uses VMEMMAP_VADDR. It is not defined on PPC64, but it looks
like PPC64 supports VMEMMAP flag and machdep->machspec->vmemmap_base is
it, so this patch also defines it for PPC64. This might need some help
from PPC folks.
Signed-off-by: Kazuhito Hagio <k-hagio(a)ab.jp.nec.com>
---
defs.h | 2 ++
memory.c | 15 +++++++++++++++
2 files changed, 17 insertions(+)
diff --git a/defs.h b/defs.h
index aa17792..84e68ca 100644
--- a/defs.h
+++ b/defs.h
@@ -3861,6 +3861,8 @@ struct efi_memory_desc_t {
#define IS_VMALLOC_ADDR(X) machdep->machspec->is_vmaddr(X)
#define KERNELBASE machdep->pageoffset
+#define VMEMMAP_VADDR (machdep->machspec->vmemmap_base)
+
#define PGDIR_SHIFT (machdep->pageshift + (machdep->pageshift -3) +
(machdep->pageshift - 2))
#define PMD_SHIFT (machdep->pageshift + (machdep->pageshift - 3))
diff --git a/memory.c b/memory.c
index 0df8ecc..0696763 100644
--- a/memory.c
+++ b/memory.c
@@ -13348,10 +13348,25 @@ is_page_ptr(ulong addr, physaddr_t *phys)
ulong nr_mem_sections;
ulong coded_mem_map, mem_map, end_mem_map;
physaddr_t section_paddr;
+#ifdef VMEMMAP_VADDR
+ ulong flags;
+#endif
if (IS_SPARSEMEM()) {
nr_mem_sections = NR_MEM_SECTIONS();
+#ifdef VMEMMAP_VADDR
+ nr = nr_mem_sections;
+ if (machdep->flags & VMEMMAP)
+ nr = pfn_to_section_nr((addr - VMEMMAP_VADDR) / SIZE(page));
+ else if (readmem(addr + OFFSET(page_flags), KVADDR, &flags,
+ sizeof(ulong), "page.flags", RETURN_ON_ERROR|QUIET))
+ nr = (flags >> (SIZE(page_flags)*8 - SECTIONS_SHIFT())
+ & ((1UL << SECTIONS_SHIFT()) - 1));
+
+ if (nr < nr_mem_sections) {
+#else
for (nr = 0; nr < nr_mem_sections ; nr++) {
+#endif
if ((sec_addr = valid_section_nr(nr))) {
coded_mem_map = section_mem_map_addr(sec_addr);
mem_map = sparse_decode_mem_map(coded_mem_map, nr);
--
1.8.3.1
--
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