The patch titled
Subject: mm: cma: allocate cma areas bottom-up
has been added to the -mm tree. Its filename is
mm-cma-allocate-cma-areas-bottom-up.patch
This patch should soon appear at
https://ozlabs.org/~akpm/mmots/broken-out/mm-cma-allocate-cma-areas-bottom-up.patch
and later at
https://ozlabs.org/~akpm/mmotm/broken-out/mm-cma-allocate-cma-areas-bottom-up.patch
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From: Roman Gushchin <guro@xxxxxx>
Subject: mm: cma: allocate cma areas bottom-up
Currently cma areas without a fixed base are allocated close to the end of
the node. This placement is sub-optimal because of compaction: it brings
pages into the cma area. In particular, it can bring in hot executable
pages, even if there is a plenty of free memory on the machine. This
results in cma allocation failures.
Instead let's place cma areas close to the beginning of a node. In this
case the compaction will help to free cma areas, resulting in better cma
allocation success rates.
If there is enough memory let's try to allocate bottom-up starting with
4GB to exclude any possible interference with DMA32. On smaller machines
or in a case of a failure, stick with the old behavior.
16GB vm, 2GB cma area:
With this patch:
[ 0.000000] Command line: root=/dev/vda3 rootflags=subvol=/root systemd.unified_cgroup_hierarchy=1 enforcing=0 console=ttyS0,115200 hugetlb_cma=2G
[ 0.002928] hugetlb_cma: reserve 2048 MiB, up to 2048 MiB per node
[ 0.002930] cma: Reserved 2048 MiB at 0x0000000100000000
[ 0.002931] hugetlb_cma: reserved 2048 MiB on node 0
Without this patch:
[ 0.000000] Command line: root=/dev/vda3 rootflags=subvol=/root systemd.unified_cgroup_hierarchy=1 enforcing=0 console=ttyS0,115200 hugetlb_cma=2G
[ 0.002930] hugetlb_cma: reserve 2048 MiB, up to 2048 MiB per node
[ 0.002933] cma: Reserved 2048 MiB at 0x00000003c0000000
[ 0.002934] hugetlb_cma: reserved 2048 MiB on node 0
v2:
- switched to memblock_set_bottom_up(true), by Mike
- start with 4GB, by Mike
Link: https://lkml.kernel.org/r/20201217201214.3414100-1-guro@xxxxxx
Signed-off-by: Roman Gushchin <guro@xxxxxx>
Reviewed-by: Mike Rapoport <rppt@xxxxxxxxxxxxx>
Cc: Wonhyuk Yang <vvghjk1234@xxxxxxxxx>
Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/cma.c | 16 ++++++++++++++++
1 file changed, 16 insertions(+)
--- a/mm/cma.c~mm-cma-allocate-cma-areas-bottom-up
+++ a/mm/cma.c
@@ -336,6 +336,22 @@ int __init cma_declare_contiguous_nid(ph
limit = highmem_start;
}
+ /*
+ * If there is enough memory, try a bottom-up allocation first.
+ * It will place the new cma area close to the start of the node
+ * and guarantee that the compaction is moving pages out of the
+ * cma area and not into it.
+ * Avoid using first 4GB to not interfere with constrained zones
+ * like DMA/DMA32.
+ */
+ if (!memblock_bottom_up() &&
+ memblock_end >= SZ_4G + size) {
+ memblock_set_bottom_up(true);
+ addr = memblock_alloc_range_nid(size, alignment, SZ_4G,
+ limit, nid, true);
+ memblock_set_bottom_up(false);
+ }
+
if (!addr) {
addr = memblock_alloc_range_nid(size, alignment, base,
limit, nid, true);
_
Patches currently in -mm which might be from guro@xxxxxx are
mm-slub-call-account_slab_page-after-slab-page-initialization.patch
mm-memcg-slab-pre-allocate-obj_cgroups-for-slab-caches-with-slab_account.patch
mm-cma-allocate-cma-areas-bottom-up.patch
mm-cma-allocate-cma-areas-bottom-up-fix.patch
memblock-do-not-start-bottom-up-allocations-with-kernel_end.patch
mm-vmstat-fix-proc-sys-vm-stat_refresh-generating-false-warnings.patch
mm-vmstat-fix-proc-sys-vm-stat_refresh-generating-false-warnings-fix.patch
