Re: [Qemu-devel] [PATCH v7 08/35] exec: allow memory to be allocated from any kind of path

[Xiao Guangrong <guangrong.xiao@linux.intel.com>]

On 11/04/2015 07:00 AM, Eduardo Habkost wrote:
> On Mon, Nov 02, 2015 at 05:13:10PM +0800, Xiao Guangrong wrote:
>> Currently file_ram_alloc() is designed for hugetlbfs, however, the memory
>> of nvdimm can come from either raw pmem device eg, /dev/pmem, or the file
>> locates at DAX enabled filesystem
>>
>> So this patch let it work on any kind of path
>>
>> Signed-off-by: Xiao Guangrong <guangrong.xiao@linux.intel.com>
>> ---
>>   exec.c | 24 ++++++++++++------------
>>   1 file changed, 12 insertions(+), 12 deletions(-)
>>
>> diff --git a/exec.c b/exec.c
>> index 9de38be..9075f4d 100644
>> --- a/exec.c
>> +++ b/exec.c
>> @@ -1184,25 +1184,25 @@ static void *file_ram_alloc(RAMBlock *block,
>>       char *c;
>>       void *area;
>>       int fd;
>> -    uint64_t hpagesize;
>> +    uint64_t pagesize;
>>       Error *local_err = NULL;
>>
>> -    hpagesize = qemu_file_get_page_size(path, &local_err);
>> +    pagesize = qemu_file_get_page_size(path, &local_err);
>>       if (local_err) {
>>           error_propagate(errp, local_err);
>>           goto error;
>>       }
>>
>> -    if (hpagesize == getpagesize()) {
>> -        fprintf(stderr, "Warning: path not on HugeTLBFS: %s\n", path);
>> +    if (pagesize == getpagesize()) {
>> +        fprintf(stderr, "Memory is not allocated from HugeTlbfs.\n");
>
> If the point of this patch is to allow file_ram_alloc() to not be
> specific to hugetlbfs anymore, this warning can simply go away.
>
> (And in case if you really want to keep the warning, I don't see the
> point of the changes you made to it.)
>

This is the history why we did it like this:
https://lists.gnu.org/archive/html/qemu-devel/2015-10/msg02862.html

Q:
| What this *actually* is trying to warn against is that
| mapping a regular file (as opposed to hugetlbfs)
| means transparent huge pages don't work.

| So I don't think we should drop this warning completely.
| Either let's add the nvdimm magic, or simply check the
| page size.

A:
| Check the page size sounds good, will check:
| if (pagesize != getpagesize()) {
|        ...print something...
|}

| I agree with you that showing the info is needed, however,
| 'Warning' might scare some users, how about drop this word or
| just show　“Memory is not allocated from HugeTlbfs”?