Messages in this thread | | | Date | Sun, 21 May 2006 23:23:51 +0100 (IST) | From | Mel Gorman <> | Subject | Re: [PATCH 4/6] Have x86_64 use add_active_range() and free_area_init_nodes |
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On Sun, 21 May 2006, Andrew Morton wrote:
> Mel Gorman <mel@csn.ul.ie> wrote: >> > >>> Anyway, I just don't get how this code can work. We have an e820 map with >>> up to 128 entries (this machine has ten) and we're trying to scrunch that >>> all into the four-entry early_node_map[]. >>> >> >> Missing E820MAX was a mistake. On x86_64, CONFIG_MAX_ACTIVE_REGIONS should >> have been used. I didn't expect x86_64 to have so many memory holes. > > x86 uses 128 e820 slots too. >
That is true, but with x86, I am not expecting many regions. For flatmem, only one region will be registered. For NUMA, I would expect one registration per node *unless* SRAT is being used. With SRAT, MAXCHUNKS regions at most with is 4 * MAX_NUMNODES.
>> >>> On my little x86 PC: >>> >>> BIOS-provided physical RAM map: >>> BIOS-e820: 0000000000000000 - 000000000009bc00 (usable) >>> BIOS-e820: 000000000009bc00 - 000000000009c000 (reserved) >>> BIOS-e820: 00000000000e0000 - 0000000000100000 (reserved) >>> BIOS-e820: 0000000000100000 - 000000000ffc0000 (usable) >>> BIOS-e820: 000000000ffc0000 - 000000000fff8000 (ACPI data) >>> BIOS-e820: 000000000fff8000 - 0000000010000000 (ACPI NVS) >>> BIOS-e820: 00000000fec00000 - 00000000fec01000 (reserved) >>> BIOS-e820: 00000000fee00000 - 00000000fee01000 (reserved) >>> BIOS-e820: 00000000ffb80000 - 00000000ffc00000 (reserved) >>> BIOS-e820: 00000000fff00000 - 0000000100000000 (reserved) >>> 0MB HIGHMEM available. >>> 255MB LOWMEM available. >>> found SMP MP-table at 000ff780 >>> Range (nid 0) 0 -> 65472, max 4 >>> On node 0 totalpages: 65472 >>> DMA zone: 4096 pages, LIFO batch:0 >>> Normal zone: 61376 pages, LIFO batch:15 >>> >>> So here, the architecture code only called add_active_range() the once, for >>> the entire memory map. >> >> Because in this case, the architecture reported that there was just one >> range of available pages with no holes. > > So.. we're registering a simgle blob of pfns which includes the "reserved" > memory as well as the "ACPI data" and the "ACPI NVS" (with an apparent > off-by-one here). >
The off-by-one is a surprise. On this machine, it must be because the arch-specific code calculated highend_pfn wrong. I don't use the e820 on i386 because it didn't seem necessary.
> How come the machine still works? I guess the architecture went and marked > those pfns reserved. >
Yes, that is what I'd expect to happen. The ranges are registered and a memmap allocated but the freeing of memory from bootmem is still the same on i386. For i386, my patchset reports the same size of zones and start_pfn on each node so there should be no difference in the end result between my code and the arch-specific initialisation.
>>> If so, perhaps the bug is that the x86_64 code isn't doing that. And that >> > x86 isn't doing it for some people either. >> > >> >> I'm hoping in this case that having MAX_ACTIVE_REGIONS match E820MAX will >> fix the issue on your machine. > > I expect it will. > > One does wonder whether it's worth all this fuss though. It's only a > 24-byte structure and it's all thrown away in free_initmem(). One _could_ > just go and do > > #define MAX_ACTIVE_REGIONS 10000 > > and be happy. >
I could, but I thought I'd be shot for trying something like that. A fixed value of 128 would cover the largest tables I'm aware of on all architectures. Should I just set that fixed value?
>> I'm still confused why Christian's failed >> to boot with the patch backed out though. > > He didn't get any "Too many memory regions" messages, so it's something > different. > > Maybe he hit my off-by-one on his "ACPI data"? >
Possibly but the off-by-one error for you was on x86 not x86_64 and I suspect that highend_pfn was wrong in this case. I'll be checking tomorrow where I can see an off-by-one error.
> hm, I didn't mention this in the earlier email. On my x86 I have > > BIOS-provided physical RAM map: > BIOS-e820: 0000000000000000 - 000000000009bc00 (usable) > BIOS-e820: 000000000009bc00 - 000000000009c000 (reserved) > BIOS-e820: 00000000000e0000 - 0000000000100000 (reserved) > BIOS-e820: 0000000000100000 - 000000000ffc0000 (usable) > BIOS-e820: 000000000ffc0000 - 000000000fff8000 (ACPI data) > BIOS-e820: 000000000fff8000 - 0000000010000000 (ACPI NVS) > BIOS-e820: 00000000fec00000 - 00000000fec01000 (reserved) > BIOS-e820: 00000000fee00000 - 00000000fee01000 (reserved) > BIOS-e820: 00000000ffb80000 - 00000000ffc00000 (reserved) > BIOS-e820: 00000000fff00000 - 0000000100000000 (reserved) > > I added some debug and saw that add_active_range() was getting a > start_pfn=0 and an end_pfn which corresponds with 0x0fffc000. So my "ACPI > NVS" is getting chopped off. >
Yes. However, this just means that the memory for that the PFN range will not be backed by memmap. This would only be a problem if free_bootmem() is called on those range of pages. If that was happening, I would be expecting oops early or bad_page reports during the boot process.
> If Christian is seeing a similar thing then his "ACPI data" will be getting > only part-registered. > > I'd suggest that the next rev be liberal in its printking. This is the > debug patch I used: >
I also have an old debug patch that was very printk happy. I will dust it off and add it with the additional information from your patch.
> mm/page_alloc.c | 25 +++++++++++++++++++++---- > 1 file changed, 21 insertions(+), 4 deletions(-) > > diff -puN mm/page_alloc.c~a mm/page_alloc.c > --- devel/mm/page_alloc.c~a 2006-05-20 13:19:58.000000000 -0700 > +++ devel-akpm/mm/page_alloc.c 2006-05-20 13:20:42.000000000 -0700 > @@ -2463,22 +2463,36 @@ void __init add_active_range(unsigned in > unsigned long end_pfn) > { > unsigned int i; > - printk(KERN_DEBUG "Range (%d) %lu -> %lu\n", nid, start_pfn, end_pfn); > + > + printk("Range (nid %d) %lu -> %lu, max %d\n", > + nid, start_pfn, end_pfn, MAX_ACTIVE_REGIONS - 1); > > /* Merge with existing active regions if possible */ > for (i = 0; early_node_map[i].end_pfn; i++) { > - if (early_node_map[i].nid != nid) > + printk("i=%d early_node_map[i].nid=%d " > + "early_node_map[i].start_pfn=%lu " > + "early_node_map[i].end_pfn=%lu", > + i, early_node_map[i].nid, > + early_node_map[i].start_pfn, > + early_node_map[i].end_pfn); > + > + if (early_node_map[i].nid != nid) { > + printk(" continue 1\n"); > continue; > + } > > /* Skip if an existing region covers this new one */ > if (start_pfn >= early_node_map[i].start_pfn && > - end_pfn <= early_node_map[i].end_pfn) > + end_pfn <= early_node_map[i].end_pfn) { > + printk(" return 1\n"); > return; > + } > > /* Merge forward if suitable */ > if (start_pfn <= early_node_map[i].end_pfn && > end_pfn > early_node_map[i].end_pfn) { > early_node_map[i].end_pfn = end_pfn; > + printk(" return 2\n"); > return; > } > > @@ -2486,13 +2500,16 @@ void __init add_active_range(unsigned in > if (start_pfn < early_node_map[i].end_pfn && > end_pfn >= early_node_map[i].start_pfn) { > early_node_map[i].start_pfn = start_pfn; > + printk(" return 3\n"); > return; > } > + printk("\n"); > } > > /* Leave last entry NULL, we use range.end_pfn to terminate the walk */ > if (i >= MAX_ACTIVE_REGIONS - 1) { > - printk(KERN_ERR "Too many memory regions, truncating\n"); > + printk(KERN_ERR "More than %d memory regions, truncating\n", > + MAX_ACTIVE_REGIONS - 1); > return; > } > > _ >
-- Mel Gorman Part-time Phd Student Linux Technology Center University of Limerick IBM Dublin Software Lab - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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