Hi Bakari,
On 12-Sep-17 4:41 AM, 912873551 at qq.com (白长敏) wrote:
Hi Jim,
Thank you for reply, i understand it, but i still have two doubts.
1) if i have > 1 DPDK application on a machine, i can use the parameter
"--file-prefix" to distinguish, it can work even if have not flock.
That's not entirely correct. DPDK will attempt to clean up *all*
hugepage files it encounters, not just those that are designated as "its
own" via the --file-prefix [1]. This is because hugepages are not freed
back to the OS unless its backing file in hugetlbfs is removed from the
system, so DPDK needs to clear out any pre-existing hugepage files in
order to successfully allocate any hugepages for its use.
2) If I understand correctly, in the "map_all_hugepages()", after making the shared
flock, close(fd), that is to free the flock. Then, in the "clear_hugedir()", it equal to
have not flock ?
You are correct that normally, closing the file descriptor would release
the lock. However, we're also doing an mmap() call on that fd [2], which
duplicates the descriptor, and therefore we continue to hold a lock to
that file.
Quote from mmap() man page [3]:
"The mmap() function shall add an extra reference to the file associated
with the file descriptor fildes which is not removed by a subsequent
close() on that file descriptor. This reference shall be removed when
there are no more mappings to the file."
[1]
http://www.dpdk.org/browse/dpdk/tree/lib/librte_eal/linuxapp/eal/eal_hugepage_info.c#n192
[2]
http://www.dpdk.org/browse/dpdk/tree/lib/librte_eal/linuxapp/eal/eal_memory.c#n505
[3] https://linux.die.net/man/3/mmap
------------------ ???? ------------------
???: "Jim Thompson";<jim at netgate.com>;
????: 2017?9?12?(???) ??11:10
???: "???"<912873551 at qq.com>;
??: "dev"<dev at dpdk.org>;
??: Re: [dpdk-dev] About the shared flock for hugepage files
Bakari,
This is so you can have > 1 DPDK application on a machine and they won't use
each other's hugepages.
See, for example the comments in clear_hugedir()
http://dpdk.org/browse/dpdk/tree/lib/librte_eal/linuxapp/eal/eal_hugepage_info.c#n198
Jim
On Sep 11, 2017, at 9:16 PM, ??? <912873551 at qq.com> wrote:
Hi, everyone,
I'm a developer from china, now i have a problem is about the shared flock for
hugepage files in the function of "map_all_hugepages()".
as follows:
---------------------------------------------------------------------------------------------------
/* set shared flock on the file. */
if (flock(fd, LOCK_SH | LOCK_NB) == -1) {
RTE_LOG(DEBUG, EAL, "%s(): Locking file failed:%s \n", __func__,
strerror(errno));
close(fd);
return i;
}
close(fd);
--------------------------------------------------------------------------------------------------
there, it gives a shared flock to each hugepage file in /mnt/huge, and close it
right away.
it makes me puzzled. Why? What doing that is for?
I'm looking forward to your reply, thank you very much.
best regards,
Bakari.
--
Thanks,
Anatoly
