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
[guro@fb.com: whitespace fix, per Mike]
Link: https://lkml.kernel.org/r/20201221170551.GB3428478@carbon.DHCP.thefacebook.com
[guro@fb.com: fix 32-bit warnings]
Link: https://lkml.kernel.org/r/20201223163537.GA4011967@carbon.DHCP.thefacebook.com
[guro@fb.com: fix 32-bit systems]
[akpm@linux-foundation.org: build fix]
Link: https://lkml.kernel.org/r/20201217201214.3414100-1-guro@fb.com
Signed-off-by: Roman Gushchin <guro@fb.com>
Reviewed-by: Mike Rapoport <rppt@linux.ibm.com>
Cc: Wonhyuk Yang <vvghjk1234@gmail.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: Michal Hocko <mhocko@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
1 file changed