jemalloc: set LG_VADDR to 64 on amd64
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Authored by kib on Mon, Sep 16, 11:10 PM.

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alc
markj
andrew
emaste

Summary

The current value 48 causes immediate breakage on la57 kernels. In principle, the value can be increased to 57, but I do not see a reason.

With this change, and the series of fixes to the trampoline, I can boot la57 on real hardware.

PS. Arm64 would need a similar fix.

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rG FreeBSD src repository

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kib created this revision.Mon, Sep 16, 11:10 PM

Herald added a subscriber: imp. · View Herald TranscriptMon, Sep 16, 11:10 PM

kib requested review of this revision.Mon, Sep 16, 11:10 PM

I don't think you'll see any difference between 57 and 64.

It looks like LG_VADDR is used to decide which bits in an internal pointer can be reused. On arm64 if the value is at most 56 then RTREE_LEAF_COMPACT is defined so parts of the pointer are reused, if it's 57 then it's not and struct rtree_leaf_elm_s pulls the index and slab bit out.

On arm64 the value could be 52 for when FEAT_LPA2 is implemented.

Do you see any performance or memory usage change with this?

In D46686#1064294, @andrew wrote:

I don't think you'll see any difference between 57 and 64.

It looks like LG_VADDR is used to decide which bits in an internal pointer can be reused. On arm64 if the value is at most 56 then RTREE_LEAF_COMPACT is defined so parts of the pointer are reused, if it's 57 then it's not and struct rtree_leaf_elm_s pulls the index and slab bit out.

On arm64 the value could be 52 for when FEAT_LPA2 is implemented.

Do you see any performance or memory usage change with this?

Machine which I have is unusable for any perf work (BIOS is too broken). Perhaps I should add an option for small/large jemalloc VADDR. default to large?

Add build option to revert back to 48 bit wide.

Herald added a subscriber: bdrewery. · View Herald TranscriptThu, Sep 19, 6:04 PM

alc added inline comments.Fri, Sep 20, 4:30 AM

tools/build/options/WITH_LG_VADDR_WIDE
3

Fix grammar in the option' description.

emaste added inline comments.Fri, Sep 20, 12:03 PM

share/mk/src.opts.mk
365–368	I don't think we generally have options that have a default on one arch and do not exist on other archs, ping @imp What does `make makeman` think of this? This will presumably be coming to at least arm64 as well it seems, and I imagine we should just have a MI on-by-default option for it.