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 [guro@xxxxxx: whitespace fix, per Mike] Link: https://lkml.kernel.org/r/20201221170551.GB3428478@xxxxxxxxxxxxxxxxxxxxxxxxxxx [guro@xxxxxx: fix 32-bit warnings] Link: https://lkml.kernel.org/r/20201223163537.GA4011967@xxxxxxxxxxxxxxxxxxxxxxxxxxx [guro@xxxxxx: fix 32-bit systems] [akpm@xxxxxxxxxxxxxxxxxxxx: build fix] 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 | 17 +++++++++++++++++ 1 file changed, 17 insertions(+) --- a/mm/cma.c~mm-cma-allocate-cma-areas-bottom-up +++ a/mm/cma.c @@ -336,6 +336,23 @@ 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. + */ +#ifdef CONFIG_PHYS_ADDR_T_64BIT + 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); + } +#endif + if (!addr) { addr = memblock_alloc_range_nid(size, alignment, base, limit, nid, true); _
