Re: [PATCH] libibverbs: Add huge page support to ibv_madvise_range()

[Roland Dreier <rdreier-FYB4Gu1CFyUAvxtiuMwx3w@public.gmane.org>]

 > ibv_reg_mr() fails to register a memory region allocated on huge page and not
 > the default page size. This happens because ibv_madvise_range() aligns memory
 > region to the default system page size before calling to madvise() which fails
 > with EINVAL error. madvise() fails because it expects that the start and end
 > pointer of the memory range be huge page aligned.

Seems unfortunate.  I wonder if there's a way the kernel madvise could
help us here?

 > +/*
 > + * Get the kernel default huge page size.
 > + */
 > +static int get_huge_page_size()
 > +{
 > +	int fd;
 > +	char buf[MEMINFO_SIZE];
 > +	int mem_file_len;
 > +	char *p_hpage_val = NULL;
 > +	char *end_pointer = NULL;
 > +	char file_name[] = "/proc/meminfo";
 > +	const char label[] = "Hugepagesize:";
 > +	int ret_val = 0;
 > +
 > +	fd = open(file_name, O_RDONLY);
 > +	if (fd < 0)
 > +		return fd;
 > +
 > +	mem_file_len = read(fd, buf, sizeof(buf) - 1);
 > +
 > +	close(fd);
 > +	if (mem_file_len < 0)
 > +		return mem_file_len;
 > +
 > +	buf[mem_file_len] = '\0';
 > +
 > +	p_hpage_val = strstr(buf, label);
 > +	if (!p_hpage_val) {
 > +		errno = EINVAL;
 > +		return -1;
 > +	}
 > +	p_hpage_val += strlen(label);
 > +
 > +	errno = 0;
 > +	ret_val = strtol(p_hpage_val, &end_pointer, 0);
 > +
 > +	if (errno != 0)
 > +		return -1;
 > +
 > +	return ret_val * 1024;
 > +}

This seems to duplicate but only partially a similar function from
libhugetlbfs.  Is there any way we can just use that directly?  eg
libhugetlbfs handles the case where there are multiple huge page sizes
(and that exists even on mainstream x86 with 2MB and 1GB pages possible
on the same system).

 - R.
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