Re: [PATCH v3 0/5] optimize memblock_next_valid_pfn and early_pfn_valid

[Wei Yang]

On Sun, Mar 25, 2018 at 08:02:14PM -0700, Jia He wrote:
>Commit b92df1de5d28 ("mm: page_alloc: skip over regions of invalid pfns
>where possible") tried to optimize the loop in memmap_init_zone(). But
>there is still some room for improvement.
>
>Patch 1 remain the memblock_next_valid_pfn when CONFIG_HAVE_ARCH_PFN_VALID
>        is enabled
>Patch 2 optimizes the memblock_next_valid_pfn()
>Patch 3~5 optimizes the early_pfn_valid(), I have to split it into parts
>        because the changes are located across subsystems.
>
>I tested the pfn loop process in memmap_init(), the same as before.
>As for the performance improvement, after this set, I can see the time
>overhead of memmap_init() is reduced from 41313 us to 24345 us in my
>armv8a server(QDF2400 with 96G memory).
>
>Attached the memblock region information in my server.
>[   86.956758] Zone ranges:
>[   86.959452]   DMA      [mem 0x0000000000200000-0x00000000ffffffff]
>[   86.966041]   Normal   [mem 0x0000000100000000-0x00000017ffffffff]
>[   86.972631] Movable zone start for each node
>[   86.977179] Early memory node ranges
>[   86.980985]   node   0: [mem 0x0000000000200000-0x000000000021ffff]
>[   86.987666]   node   0: [mem 0x0000000000820000-0x000000000307ffff]
>[   86.994348]   node   0: [mem 0x0000000003080000-0x000000000308ffff]
>[   87.001029]   node   0: [mem 0x0000000003090000-0x00000000031fffff]
>[   87.007710]   node   0: [mem 0x0000000003200000-0x00000000033fffff]
>[   87.014392]   node   0: [mem 0x0000000003410000-0x000000000563ffff]
>[   87.021073]   node   0: [mem 0x0000000005640000-0x000000000567ffff]
>[   87.027754]   node   0: [mem 0x0000000005680000-0x00000000056dffff]
>[   87.034435]   node   0: [mem 0x00000000056e0000-0x00000000086fffff]
>[   87.041117]   node   0: [mem 0x0000000008700000-0x000000000871ffff]
>[   87.047798]   node   0: [mem 0x0000000008720000-0x000000000894ffff]
>[   87.054479]   node   0: [mem 0x0000000008950000-0x0000000008baffff]
>[   87.061161]   node   0: [mem 0x0000000008bb0000-0x0000000008bcffff]
>[   87.067842]   node   0: [mem 0x0000000008bd0000-0x0000000008c4ffff]
>[   87.074524]   node   0: [mem 0x0000000008c50000-0x0000000008e2ffff]
>[   87.081205]   node   0: [mem 0x0000000008e30000-0x0000000008e4ffff]
>[   87.087886]   node   0: [mem 0x0000000008e50000-0x0000000008fcffff]
>[   87.094568]   node   0: [mem 0x0000000008fd0000-0x000000000910ffff]
>[   87.101249]   node   0: [mem 0x0000000009110000-0x00000000092effff]
>[   87.107930]   node   0: [mem 0x00000000092f0000-0x000000000930ffff]
>[   87.114612]   node   0: [mem 0x0000000009310000-0x000000000963ffff]
>[   87.121293]   node   0: [mem 0x0000000009640000-0x000000000e61ffff]
>[   87.127975]   node   0: [mem 0x000000000e620000-0x000000000e64ffff]
>[   87.134657]   node   0: [mem 0x000000000e650000-0x000000000fffffff]
>[   87.141338]   node   0: [mem 0x0000000010800000-0x0000000017feffff]
>[   87.148019]   node   0: [mem 0x000000001c000000-0x000000001c00ffff]
>[   87.154701]   node   0: [mem 0x000000001c010000-0x000000001c7fffff]
>[   87.161383]   node   0: [mem 0x000000001c810000-0x000000007efbffff]
>[   87.168064]   node   0: [mem 0x000000007efc0000-0x000000007efdffff]
>[   87.174746]   node   0: [mem 0x000000007efe0000-0x000000007efeffff]
>[   87.181427]   node   0: [mem 0x000000007eff0000-0x000000007effffff]
>[   87.188108]   node   0: [mem 0x000000007f000000-0x00000017ffffffff]

Hi, Jia

I haven't taken a deep look into your code, just one curious question on your
memory layout.

The log above is printed out in free_area_init_nodes(), which iterates on
memblock.memory and prints them. If I am not wrong, memory regions added to
memblock.memory are ordered and merged if possible.

While from your log, I see many regions could be merged but are isolated. For
example, the last two region:

  node   0: [mem 0x000000007eff0000-0x000000007effffff]
  node   0: [mem 0x000000007f000000-0x00000017ffffffff]

So I am curious why they are isolated instead of combined to one.

>From the code, the possible reason is the region's flag differs from each
other. If you have time, would you mind taking a look into this?

-- 
Wei Yang
Help you, Help me