Re: [dpdk-dev] [PATCH v3] mem: command line option to delete hugepage backing files

[Sergio Gonzalez Monroy <sergio.gonzalez.monroy@intel.com>]

On 21/10/2015 17:34, Bruce Richardson wrote:
> On Wed, Oct 21, 2015 at 04:22:45PM +0000, shesha Sreenivasamurthy (shesha) wrote:
>> When an application using huge-pages crash or exists, the hugetlbfs
>> backing files are not cleaned up. This is a patch to clean those files.
>> There are multi-process DPDK applications that may be benefited by those
>> backing files. Therefore, I have made that configurable so that the
>> application that does not need those backing files can remove them, thus
>> not changing the current default behavior. The application itself can
>> clean it up, however the rationale behind DPDK cleaning it up is, DPDK
>> created it and therefore, it is better it unlinks it.
>>
>> Signed-off-by: Shesha Sreenivasamurthy <shesha@cisco.com>
>> ---
>>   lib/librte_eal/common/eal_common_options.c | 12 ++++++++++++
>>   lib/librte_eal/common/eal_internal_cfg.h   |  1 +
>>   lib/librte_eal/common/eal_options.h        |  2 ++
>>   lib/librte_eal/linuxapp/eal/eal_memory.c   | 30
>> ++++++++++++++++++++++++++++++
>>   4 files changed, 45 insertions(+)
>>
> <snip>
>> +static int
>> +unlink_hugepage_files(struct hugepage_file *hugepg_tbl,
>> +		unsigned num_hp_info)
>> +{
>> +	unsigned socket, size;
>> +	int page, nrpages = 0;
>> +
>> +	/* get total number of hugepages */
>> +	for (size = 0; size < num_hp_info; size++)
>> +		for (socket = 0; socket < RTE_MAX_NUMA_NODES; socket++)
>> +			nrpages += internal_config.hugepage_info[size].num_pages[socket];
>> +
>> +	for (page = 0; page < nrpages; page++) {
>> +		struct hugepage_file *hp = &hugepg_tbl[page];
>> +		if (hp->final_va != NULL && unlink(hp->filepath)) {
>> +			RTE_LOG(WARNING, EAL, "%s(): Removing %s failed: %s\n",
>> +				__func__, hp->filepath, strerror(errno));
>> +		}
>> +	}
>> +	return 0;
>> +}
>> +
>>   /*
>>    * unmaps hugepages that are not going to be used. since we originally
>> allocate
>>    * ALL hugepages (not just those we need), additional unmapping needs to
>> be done.
>> @@ -1289,6 +1311,14 @@ rte_eal_hugepage_init(void)
>>   		goto fail;
>>   	}
>>   
>> +	/* free the hugepage backing files */
>> +	if (internal_config.hugepage_unlink &&
>> +		unlink_hugepage_files(tmp_hp,
>> +			internal_config.num_hugepage_sizes) < 0) {
>> +			RTE_LOG(ERR, EAL, "Unlinking hugepage backing files failed!\n");
>> +		goto fail;
>> +	}
>> +
> Sorry for the late comment, but...
>
> Rather than adding a whole new function to be called here, can the same effect
> not be got by adding in 2/3 lines like:
> 	if (internal_config.hugepage_unlink)
> 		unlink(hugetlb[i].filepath)
>
> at line 409 of eal_memory.c where were have done our final mmap of the file.
> [You also need the same couple of lines for the 32-bit special case at line 351].
> It would be a shorter diff.
>
> /Bruce
If you wanted to avoid the extra function call, I might be cleaner to 
just unlink all files when
doing unmap_all_hugepages_orig.
My two cents: I think it would be easier to read/debug having a function 
that "unlinks files" instead
of unlinking files at different points in map_all_hugepages.

Unfortunately the proposed approach does not work for all cases:
- If we have single file segment, map_all_hugepages does not get call a 
second time, instead we call
   remap_all_hugepages
- If we use options -m or --socket-mem, because unmap_unneeded_hugepages 
does not expect files
   already unlinked, it will fail when trying to unlink unneeded 
hugepage files.

The current patch would work as we only unlink after 
unmap_unneeded_hugepages.

Sergio