[Crash-utility] [PATCH] Speed up "kmem -[sS]" by optimizing is_page_ptr()
Dave Anderson
anderson at redhat.com
Tue Feb 20 16:32:44 UTC 2018
----- Original Message -----
> Hi Dave,
>
> On 2/16/2018 4:18 PM, Dave Anderson wrote:
> ...
> >>>> OK, I understand your point. But what concerns me is that the
> >>>> function's
> >>>> purpose is to absolutely identify whether the incoming page structure
> >>>> address
> >>>> is a correct page structure address. But if an invalid address gets
> >>>> passed
> >>>> into is_page_ptr(), your patch would take the invalid address, calculate
> >>>> an
> >>>> invalid "nr", and continue from there, right?
> >>
> >> Yes, if an invalid "nr" is the number where section does not exist,
> >> valid_section_nr() would return 0. Even if it is the number where section
> >> exists by accident, the invalid "addr" is not between mem_map and
> >> end_mem_map,
> >> or not page-aligned, because if so, it is a page structure address.
> >>
> >> Also without this patch, when an invalid address comes, the loop could
> >> tries
> >> many invalid "nr"s less than NR_MEM_SECTIONS().
> >>
> >> I hope this answers your concern..
> >>
> >>>
> >>> Another suggestion/question -- if is_page_ptr() is called with a NULL
> >>> phys
> >>> argument (as is done most of the time), could it skip the "if
> >>> IS_SPARSEMEM()"
> >>> section at the top, and still utilize the part at the bottom, where it
> >>> walks
> >>> through the vt->node_table[x] array? I'm not sure about the "ppend"
> >>> calculation
> >>> though -- even if there are holes in the node's address space, is it
> >>> still
> >>> a
> >>> contiguous chunk of page structure addresses per-node?
> >>
> >> I'm still investigating and not sure yet, but I think that SPASEMEM uses
> >> mem_section instead of node_mem_map means page structures could be
> >> non-contignuous per-node according to architecture or condition.
> >>
> >> typedef struct pglist_data {
> >> ...
> >> #ifdef CONFIG_FLAT_NODE_MEM_MAP /* means !SPARSEMEM */
> >> struct page *node_mem_map;
> >>
> >> I'll continue to check it.
> >
> > You are right, but in the case where pglist_data.node_mem_map does *not*
> > exist,
> > the crash utility initializes each vt->node_table[node].mem_map with the
> > node's
> > starting mem_map address by using the return value from phys_to_page() of
> > the
> > node's starting physical address -- which uses the sparsemem functions.
> >
> > The question is whether the current "ppend" calculation is correct for the
> > last
> > physical page in a node. If it is not correct, then perhaps an
> > "mem_map_end" value
> > can be added to the node_table structure, initialized by using
> > phys_to_page() to get
> > the page address of the last physical address in the node. And then in
> > that case, the
> > question is whether the mem_map range of virtual addresses are contiguous
> > -- even if
> > there are holes in the mem_map virtual address range.
>
> "node_size" is set to pglist_data.node_spanned_pages, which includes holes.
> So I think that if VMEMMAP, which a page address is linear against its pfn,
> the current "ppend" calculation is correct for the last page in a node.
> But if not VMEMMAP, since there is no guarantee of the linearity, the
> calculation could be incorrect.
>
> I found an example with RHEL5:
>
> crash> help -o
> ...
> size_table:
> page: 56
> ...
> crash> kmem -n
> NODE SIZE PGLIST_DATA BOOTMEM_DATA NODE_ZONES
> 0 524279 ffff810000014000 ffffffff804e1900 ffff810000014000
> ffff810000014b00
> ffff810000015600
> ffff810000016100
> MEM_MAP START_PADDR START_MAPNR
> ffff8100007da000 0 0
>
> ZONE NAME SIZE MEM_MAP START_PADDR START_MAPNR
> 0 DMA 4096 ffff8100007da000 0 0
> 1 DMA32 520183 ffff810000812000 1000000 4096
> 2 Normal 0 0 0 0
> 3 HighMem 0 0 0 0
>
> -------------------------------------------------------------------
>
> NR SECTION CODED_MEM_MAP MEM_MAP PFN
> 0 ffff810009000000 ffff8100007da000 ffff8100007da000 0
> 1 ffff810009000008 ffff8100007da000 ffff81000099a000 32768
> 2 ffff810009000010 ffff8100007da000 ffff810000b5a000 65536
> 3 ffff810009000018 ffff8100007da000 ffff810000d1a000 98304 <= there is a
> 4 ffff810009000020 ffff810008901000 ffff810009001000 131072 <= mem_map gap.
> 5 ffff810009000028 ffff810008901000 ffff8100091c1000 163840
> :
> 14 ffff810009000070 ffff810008901000 ffff81000a181000 458752
> 15 ffff810009000078 ffff810008901000 ffff81000a341000 491520
> crash>
>
> In this case, the "ppend" will be
>
> 0xffff8100007da000 + (524279 * 56)
> = 0xffff8100023d9e08
>
> but it looks like the actual value is around 0xffff81000a501000.
Right, I understand that the current "ppend" calculation wouldn't work.
> And also, we can see the gap between NR=3 and 4. This means that if the
> correct "mem_map_end" is added to the node_table structure, it would be
> not enough to check whether an address is a page structure.
Why? Wouldn't it still give us an ascending range of page structure addresses
on a per-node basis? (even if there was a physical and/or virtual memory hole?)
AFAICT, for each section NR, the MEM_MAP and PFN values always increment.
Dave
> Thanks,
> Kazuhito Hagio
>
> >
> > Thanks,
> > Dave
> >
> >
> >
> >>
> >> Thanks,
> >> Kazuhito Hagio
> >>
> >>>
> >>>>
> >>>> Dave
> >>>>
> >>>>>
> >>>>>>
> >>>>>> 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?
> >>>>>
> >>>>> Given possible compatibility issues you said, I think that the way you
> >>>>> suggested
> >>>>> might well be enough for now. I'll try a method like the above.
> >>>>>
> >>>>> Thanks,
> >>>>> Kazuhito Hagio
> >>>>>
> >>>>>>
> >>>>>> 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 at 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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