#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>

#include "rnd.h"
#include "die.h"
#include "ioexact.h"
#include "ioops.h"

static int fdw = -1;

static void randombytes_weak(unsigned char *x, unsigned long long xlen)
{
	int ret;

	if (fdw == -1) {
		for (;;) {
			fdw = open(LOW_ENTROPY_SOURCE, O_RDONLY);
			if (fdw != -1)
				break;
			sleep(1);
		}
	}

	while (xlen > 0) {
		if (xlen < 1048576)
			ret = xlen;
		else
			ret = 1048576;

		ret = read(fdw, x, ret);
		if (ret < 1) {
			sleep(1);
			continue;
		}

		x += ret;
		xlen -= ret;
	}
}

static void randombytes_strong(unsigned char *x, unsigned long long xlen)
{
	int fds, ret;

	fds = open_or_die(HIG_ENTROPY_SOURCE, O_RDONLY);

	ret = read_exact(fds, x, xlen, 0);
	if (ret != xlen)
		panic("Error reading from entropy source!\n");

	close(fds);
}

int secrand(void)
{
	int ret;

	randombytes_weak((void *) &ret, sizeof(ret));

	return ret;
}

void gen_key_bytes(unsigned char *area, size_t len)
{
	randombytes_strong(area, len);
}
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<tr><th>author</th><td>Vlastimil Babka &lt;vbabka@suse.cz&gt;</td><td class='right'>2016-05-19 17:11:51 -0700</td></tr>
<tr><th>committer</th><td>Linus Torvalds &lt;torvalds@linux-foundation.org&gt;</td><td class='right'>2016-05-19 19:12:14 -0700</td></tr>
<tr><th>commit</th><td colspan='2' class='oid'><a href='/cgit.cgi/linux/net-next.git/commit/?id=a34753d275576896b06af9baa6f54bee258368c2'>a34753d275576896b06af9baa6f54bee258368c2</a> (<a href='/cgit.cgi/linux/net-next.git/patch/?id=a34753d275576896b06af9baa6f54bee258368c2'>patch</a>)</td></tr>
<tr><th>tree</th><td colspan='2' class='oid'><a href='/cgit.cgi/linux/net-next.git/tree/?id=a34753d275576896b06af9baa6f54bee258368c2'>6cdb6beec24ff70f83c08515b5ad2b9ccf5c5580</a></td></tr>
<tr><th>parent</th><td colspan='2' class='oid'><a href='/cgit.cgi/linux/net-next.git/commit/?id=06b6640a3902d6d50c1bb4fb1f29a46b207dbf08'>06b6640a3902d6d50c1bb4fb1f29a46b207dbf08</a> (<a href='/cgit.cgi/linux/net-next.git/diff/?id=a34753d275576896b06af9baa6f54bee258368c2&amp;id2=06b6640a3902d6d50c1bb4fb1f29a46b207dbf08'>diff</a>)</td></tr></table>
<div class='commit-subject'>mm, compaction: reduce spurious pcplist drains</div><div class='commit-msg'>Compaction drains the local pcplists each time migration scanner moves
away from a cc-&gt;order aligned block where it isolated pages for
migration, so that the pages freed by migrations can merge into higher
orders.

The detection is currently coarser than it could be.  The
cc-&gt;last_migrated_pfn variable should track the lowest pfn that was
isolated for migration.  But it is set to the pfn where
isolate_migratepages_block() starts scanning, which is typically the
first pfn of the pageblock.  There, the scanner might fail to isolate
several order-aligned blocks, and then isolate COMPACT_CLUSTER_MAX in
another block.  This would cause the pcplists drain to be performed,
although the scanner didn't yet finish the block where it isolated from.

This patch thus makes cc-&gt;last_migrated_pfn handling more accurate by
setting it to the pfn of an actually isolated page in
isolate_migratepages_block().  Although practical effects of this patch
are likely low, it arguably makes the intent of the code more obvious.
Also the next patch will make async direct compaction skip blocks more
aggressively, and draining pcplists due to skipped blocks is wasteful.

Signed-off-by: Vlastimil Babka &lt;vbabka@suse.cz&gt;
Cc: Joonsoo Kim &lt;iamjoonsoo.kim@lge.com&gt;
Cc: Mel Gorman &lt;mgorman@techsingularity.net&gt;
Cc: Rik van Riel &lt;riel@redhat.com&gt;
Cc: David Rientjes &lt;rientjes@google.com&gt;
Cc: Minchan Kim &lt;minchan@kernel.org&gt;
Cc: Michal Hocko &lt;mhocko@suse.com&gt;
Signed-off-by: Andrew Morton &lt;akpm@linux-foundation.org&gt;
Signed-off-by: Linus Torvalds &lt;torvalds@linux-foundation.org&gt;
</div><div class='diffstat-header'><a href='/cgit.cgi/linux/net-next.git/diff/?id=a34753d275576896b06af9baa6f54bee258368c2'>Diffstat</a></div><table summary='diffstat' class='diffstat'><tr><td class='mode'>-rw-r--r--</td><td class='upd'><a href='/cgit.cgi/linux/net-next.git/diff/mm/compaction.c?id=a34753d275576896b06af9baa6f54bee258368c2'>mm/compaction.c</a></td><td class='right'>20</td><td class='graph'><table summary='file diffstat' width='20%'><tr><td class='add' style='width: 45.0%;'/><td class='rem' style='width: 55.0%;'/><td class='none' style='width: 0.0%;'/></tr></table></td></tr>
</table><div class='diffstat-summary'>1 files changed, 9 insertions, 11 deletions</div><table summary='diff' class='diff'><tr><td><div class='head'>diff --git a/mm/compaction.c b/mm/compaction.c