c928807f6f
OOM kills due to vastly overestimated free highatomic reserves were observed: ... invoked oom-killer: gfp_mask=0x100cca(GFP_HIGHUSER_MOVABLE), order=0 ... Node 0 Normal free:1482936kB boost:0kB min:410416kB low:739404kB high:1068392kB reserved_highatomic:1073152KB ... Node 0 Normal: 1292*4kB (ME) 1920*8kB (E) 383*16kB (UE) 220*32kB (ME) 340*64kB (E) 2155*128kB (UE) 3243*256kB (UE) 615*512kB (U) 1*1024kB (M) 0*2048kB 0*4096kB = 1477408kB The second line above shows that the OOM kill was due to the following condition: free (1482936kB) - reserved_highatomic (1073152kB) = 409784KB < min (410416kB) And the third line shows there were no free pages in any MIGRATE_HIGHATOMIC pageblocks, which otherwise would show up as type 'H'. Therefore __zone_watermark_unusable_free() underestimated the usable free memory by over 1GB, which resulted in the unnecessary OOM kill above. The comments in __zone_watermark_unusable_free() warns about the potential risk, i.e., If the caller does not have rights to reserves below the min watermark then subtract the high-atomic reserves. This will over-estimate the size of the atomic reserve but it avoids a search. However, it is possible to keep track of free pages in reserved highatomic pageblocks with a new per-zone counter nr_free_highatomic protected by the zone lock, to avoid a search when calculating the usable free memory. And the cost would be minimal, i.e., simple arithmetics in the highatomic alloc/free/move paths. Note that since nr_free_highatomic can be relatively small, using a per-cpu counter might cause too much drift and defeat its purpose, in addition to the extra memory overhead. Dependson |
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arch | ||
block | ||
certs | ||
crypto | ||
Documentation | ||
drivers | ||
fs | ||
include | ||
init | ||
io_uring | ||
ipc | ||
kernel | ||
lib | ||
LICENSES | ||
mm | ||
net | ||
rust | ||
samples | ||
scripts | ||
security | ||
sound | ||
tools | ||
usr | ||
virt | ||
.clang-format | ||
.cocciconfig | ||
.editorconfig | ||
.get_maintainer.ignore | ||
.gitattributes | ||
.gitignore | ||
.mailmap | ||
.rustfmt.toml | ||
COPYING | ||
CREDITS | ||
Kbuild | ||
Kconfig | ||
MAINTAINERS | ||
Makefile | ||
README |
Linux kernel ============ There are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. Please read Documentation/admin-guide/README.rst first. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. The formatted documentation can also be read online at: https://www.kernel.org/doc/html/latest/ There are various text files in the Documentation/ subdirectory, several of them using the reStructuredText markup notation. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.