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Channel program may spuriously fail with "memory limit exhausted"
ZFS channel programs (invoked by `zfs program`) are executed in a LUA sandbox with a limit on the amount of memory they can consume. The limit is 10MB by default, and can be raised to 100MB with the `-m` flag. If the memory limit is exceeded, the LUA program exits and the command fails with a message like `Channel program execution failed: Memory limit exhausted.` The LUA sandbox allocates memory with `vmem_alloc(KM_NOSLEEP)`, which will fail if the requested memory is not immediately available. In this case, the program fails with the same message, `Memory limit exhausted`. However, in this case the specified memory limit has not been reached, and the memory may only be temporarily unavailable. This commit changes the LUA memory allocator `zcp_lua_alloc()` to use `vmem_alloc(KM_SLEEP)`, so that we won't spuriously fail when memory is temporarily low. Instead, we rely on the system to be able to free up memory (e.g. by evicting from the ARC), and we assume that even at the highest memory limit of 100MB, the channel program will not truly exhaust the system's memory. External-issue: DLPX-71924 Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov> Reviewed-by: Ryan Moeller <ryan@iXsystems.com> Signed-off-by: Matthew Ahrens <mahrens@delphix.com> Closes #11190
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@ -722,8 +722,6 @@ static void *
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zcp_lua_alloc(void *ud, void *ptr, size_t osize, size_t nsize)
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{
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zcp_alloc_arg_t *allocargs = ud;
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int flags = (allocargs->aa_must_succeed) ?
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KM_SLEEP : (KM_NOSLEEP | KM_NORMALPRI);
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if (nsize == 0) {
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if (ptr != NULL) {
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@ -746,10 +744,7 @@ zcp_lua_alloc(void *ud, void *ptr, size_t osize, size_t nsize)
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return (NULL);
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}
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allocbuf = vmem_alloc(allocsize, flags);
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if (allocbuf == NULL) {
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return (NULL);
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}
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allocbuf = vmem_alloc(allocsize, KM_SLEEP);
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allocargs->aa_alloc_remaining -= allocsize;
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*allocbuf = allocsize;
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