Re: [discuss] Re: 32-bit dma allocations on 64-bit platforms

[Andrew Morton]

Andrew Morton <akpm@xxxxxxxx> wrote:
>
> Note that this code was sigificantly changed between 2.6.5 and 2.6.7.


Here's the default setup on a 1G ia32 box:

DMA free:4172kB min:16kB low:32kB high:48kB active:0kB inactive:0kB present:16384kB
protections[]: 8 476 540
Normal free:54632kB min:936kB low:1872kB high:2808kB active:278764kB inactive:253668kB present:901120kB
protections[]: 0 468 532
HighMem free:308kB min:128kB low:256kB high:384kB active:87972kB inactive:40300kB present:130516kB
protections[]: 0 0 64

ie:

- protect 8 pages from ZONE_DMA from a GFP_DMA allocation attempt

- protect 476 pages from ZONE_DMA from a GFP_KERNEL allocation attempt

- protect 540 pages from ZONE_DMA from a GFP_HIGHMEM allocation attempt.

etcetera.

After setting lower_zone_protection to 10:

Active:111515 inactive:65009 dirty:116 writeback:0 unstable:0 free:3290 slab:75489 mapped:52247 pagetables:446
DMA free:4172kB min:16kB low:32kB high:48kB active:0kB inactive:0kB present:16384kB
protections[]: 8 5156 5860
Normal free:8736kB min:936kB low:1872kB high:2808kB active:352780kB inactive:224972kB present:901120kB
protections[]: 0 468 1172
HighMem free:252kB min:128kB low:256kB high:384kB active:93280kB inactive:35064kB present:130516kB
protections[]: 0 0 64

It's a bit complex, and perhaps the relative levels of the various
thresholds could be tightened up.
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