Re: [Crash-utility] [PATCH] Speed up "kmem -[sS]" by optimizing is_page_ptr()

Hi Dave, Thank you for your comment! On 2/13/2018 2:33 PM, Dave Anderson wrote: > > 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. Sorry, my explanation was not enough. Please let me supplement a little. As far as I know, the count_partial() is the function which could receive the effect of this patch most. But is_page_ptr() could be called many times also through the other functions, so this will improve them, too. Moreover, the is_page_ptr()'s loop could loop NR_MEM_SECTIONS() times, which is 33554432 on x86_64(5level) if I understand correctly, in the worst case. So I thought that ideally we should improve the is_page_ptr() itself if possible, rather than find the callers which could call it many times and change them. Also, I am willing to drop the definition of VMEMMAP_VADDR for ppc64 this time.

> > 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(a)ab.jp.nec.com&gt; >> --- >> 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 >> >> -- >> Crash-utility mailing list >> Crash-utility(a)redhat.com >> https://www.redhat.com/mailman/listinfo/crash-utility >> > > -- > Crash-utility mailing list > Crash-utility(a)redhat.com > https://www.redhat.com/mailman/listinfo/crash-utility > -- Crash-utility mailing list Crash-utility(a)redhat.com https://www.redhat.com/mailman/listinfo/crash-utility