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zfs(openzfs): cap the default ARC at half of RAM for app coexistence #1487

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zfs(openzfs): cap the default ARC at half of RAM for app coexistence #1487

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12 changes: 12 additions & 0 deletions modules/open_zfs/osv/module/os/osv/zfs/arc_os.c
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Original file line number Diff line number Diff line change
Expand Up @@ -106,6 +106,18 @@ arc_default_max(uint64_t min, uint64_t allmem)
else
size = allmem / 8;

/*
* OSv: the ARC and the application share one physical address space.
* Cap the default at half of RAM for guests > 2 GiB so a large app
* (e.g. PostgreSQL with multi-GiB shared_buffers plus many backends)
* always keeps at least half the guest's memory and a checkpoint burst
* cannot drive the guest OOM. ZFS_MODULE_PARAM is a no-op on OSv, so
* zfs_arc_max cannot yet override this at boot; a future cmdline wiring
* could.
*/
if (allmem > (2ULL << 30))
size = MIN(size, allmem / 2);

return (MAX(size, min));
}

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