Messages in this thread | | | Date | Tue, 9 May 2006 12:05:05 +0100 | Subject | [PATCH 0/3] Zone boundry alignment fixes | From | Andy Whitcroft <> |
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Ok. Finally got my test bed working and got this lot tested.
To summarise the problem , the buddy allocator currently requires that the boundries between zones occur at MAX_ORDER boundries. The specific case where we were tripping up on this was in x86 with NUMA enabled. There we try to ensure that each node's stuct pages are in node local memory, in order to allow them to be virtually mapped we have to reduce the size of ZONE_NORMAL. Here we are rounding the remap space up to a large page size to allow large page TLB entries to be used. However, these are smaller than MAX_ORDER. This can lead to bad buddy merges. With VM_DEBUG enabled we detect the attempts to merge across this boundry and panic.
We have two basic options we can either apply the appropriate alignment when we make make the NUMA remap space, or we can 'fix' the assumption in the buddy allocator. The fix for the buddy allocator involves adding conditionals to the free fast path and so it seems reasonable to at least favor realigning the remap space.
Following this email are 3 patches:
zone-init-check-and-report-unaligned-zone-boundries -- introduces a zone alignement helper, and uses it to add a check to zone initialisation for unaligned zone boundries,
x86-align-highmem-zone-boundries-with-NUMA -- uses the zone alignment helper to align the end of ZONE_NORMAL after the remap space has been reserved, and
zone-allow-unaligned-zone-boundries -- modifies the buddy allocator so that we can allow unaligned zone boundries. A new configuration option is added to enable this functionality.
The first two are the fixes for alignement in x86, these fix the panics thrown when VM_DEBUG is enabled.
The last is a patch to support unaligned zone boundries. As this (re)introduces a zone check into the free hot path it seems reasonable to only enable this should it be needed; for example we never need this if we have a single zone. I have tested the failing system with this patch enabled and it also fixes the panic. I am inclined to suggest that it be included as it very clearly documents the alignment requirements for the buddy allocator.
Comments.
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