The patch titled
zone init check and report unaligned zone boundaries
has been removed from the -mm tree. Its filename is
zone-init-check-and-report-unaligned-zone-boundaries.patch
This patch was dropped because an updated version was merged
------------------------------------------------------
Subject: zone init check and report unaligned zone boundaries
From: Andy Whitcroft <apw@xxxxxxxxxxxx>
To summarise the problem, the buddy allocator currently requires that the
boundaries between zones occur at MAX_ORDER boundaries. 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 boundary 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-boundaries -- introduces
a zone alignement helper, and uses it to add a check to zone
initialisation for unaligned zone boundaries,
x86-align-highmem-zone-boundaries-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-boundaries -- modifies the buddy allocator
so that we can allow unaligned zone boundaries. 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 boundaries. 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.
This patch:
The buddy allocator has a requirement that boundaries between contigious zones
occur aligned with the the MAX_ORDER ranges. Where they do not we will
incorrectly merge pages cross zone boundaries. Add a check during zone
initialisation to warn when zones boundaries do not maintain this requirement.
The buddy allocator coelesces a newly freed page if it finds that the buddy of
that page is also free. A buddy is eligable for coelescing if the page* for
its left hand end is marked free and is complete (ie all pages in the buddy
are free). The buddy allocator takes no account of the node or zone in which
the page* is located. This places an alignment requirement zones. Where two
zones meet they must do so aligned with a MAX_ORDER range else we will pick up
buddies from both sides of the boundary and merge them into one of the zones.
This is very undesirable as it can lead to memory from the wrong zone being
handed out.
This patch adds checks during zone initialisation to check for misaligned zone
boundaries and report them.
Signed-off-by: Andy Whitcroft <apw@xxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxx>
---
include/linux/mmzone.h | 5 +++++
mm/page_alloc.c | 5 +++++
2 files changed, 10 insertions(+)
diff -puN include/linux/mmzone.h~zone-init-check-and-report-unaligned-zone-boundaries include/linux/mmzone.h
--- devel/include/linux/mmzone.h~zone-init-check-and-report-unaligned-zone-boundaries 2006-06-09 15:21:45.000000000 -0700
+++ devel-akpm/include/linux/mmzone.h 2006-06-09 15:21:45.000000000 -0700
@@ -389,6 +389,11 @@ static inline int is_dma(struct zone *zo
return zone == zone->zone_pgdat->node_zones + ZONE_DMA;
}
+static inline unsigned long zone_boundary_align_pfn(unsigned long pfn)
+{
+ return pfn & ~((1 << MAX_ORDER) - 1);
+}
+
/* These two functions are used to setup the per zone pages min values */
struct ctl_table;
struct file;
diff -puN mm/page_alloc.c~zone-init-check-and-report-unaligned-zone-boundaries mm/page_alloc.c
--- devel/mm/page_alloc.c~zone-init-check-and-report-unaligned-zone-boundaries 2006-06-09 15:21:45.000000000 -0700
+++ devel-akpm/mm/page_alloc.c 2006-06-09 15:21:45.000000000 -0700
@@ -2087,6 +2087,11 @@ static void __init free_area_init_core(s
nr_kernel_pages += realsize;
nr_all_pages += realsize;
+ if (zone_boundary_align_pfn(zone_start_pfn) !=
+ zone_start_pfn && j != 0 && size != 0)
+ printk(KERN_CRIT "node %d zone %s misaligned "
+ "start pfn\n", nid, zone_names[j]);
+
zone->spanned_pages = size;
zone->present_pages = realsize;
zone->name = zone_names[j];
_
Patches currently in -mm which might be from apw@xxxxxxxxxxxx are
zone-handle-unaligned-zone-boundaries.patch
zone-init-check-and-report-unaligned-zone-boundaries.patch
x86-align-highmem-zone-boundaries-with-numa.patch
zone-allow-unaligned-zone-boundaries.patch
zone-allow-unaligned-zone-boundaries-x86-add-zone-alignment-qualifier.patch
pg_uncached-is-ia64-only.patch
squash-duplicate-page_to_pfn-and-pfn_to_page.patch
flatmem-relax-requirement-for-memory-to-start-at-pfn-0.patch
sparsemem-record-nid-during-memory-present.patch
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