[PATCH] proc: add /proc/kpagecskip interface

[Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>]

From: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Subject: [PATCH] proc: add /proc/kpagecskip interface

This makes page pageblock skip on compaction information available
to the user-space.

Cc: Matt Mackall <mpm@selenic.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
---
Based on top of http://www.spinics.net/lists/linux-mm/msg35528.html
patch.

Example user-space usage has been added to:
https://github.com/bzolnier/pagemap-demo-ng

 fs/proc/page.c |   52 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 52 insertions(+)

Index: b/fs/proc/page.c
===================================================================
--- a/fs/proc/page.c	2012-11-29 12:06:10.408621309 +0100
+++ b/fs/proc/page.c	2012-11-29 12:11:19.760621273 +0100
@@ -339,12 +339,64 @@ static const struct file_operations proc
 	.read = kpagetype_read,
 };
 
+#ifdef CONFIG_COMPACTION
+static ssize_t kpagecskip_read(struct file *file, char __user *buf,
+			       size_t count, loff_t *ppos)
+{
+	u64 __user *out = (u64 __user *)buf;
+	struct page *ppage;
+	unsigned long src = *ppos;
+	unsigned long pfn;
+	ssize_t ret = 0;
+	u64 pcskip;
+
+	pfn = src / KPMSIZE;
+	count = min_t(unsigned long, count,
+		      ((ARCH_PFN_OFFSET + max_pfn) * KPMSIZE) - src);
+	if (src & KPMMASK || count & KPMMASK)
+		return -EINVAL;
+
+	while (count > 0) {
+		if (pfn_valid(pfn))
+			ppage = pfn_to_page(pfn);
+		else
+			ppage = NULL;
+		if (!ppage)
+			pcskip = 0;
+		else
+			pcskip = get_pageblock_skip(ppage);
+
+		if (put_user(pcskip, out)) {
+			ret = -EFAULT;
+			break;
+		}
+
+		pfn++;
+		out++;
+		count -= KPMSIZE;
+	}
+
+	*ppos += (char __user *)out - buf;
+	if (!ret)
+		ret = (char __user *)out - buf;
+	return ret;
+}
+
+static const struct file_operations proc_kpagecskip_operations = {
+	.llseek = mem_lseek,
+	.read = kpagecskip_read,
+};
+#endif
+
 static int __init proc_page_init(void)
 {
 	proc_create("kpagecount", S_IRUSR, NULL, &proc_kpagecount_operations);
 	proc_create("kpageflags", S_IRUSR, NULL, &proc_kpageflags_operations);
 	proc_create("kpageorder", S_IRUSR, NULL, &proc_kpageorder_operations);
 	proc_create("kpagetype", S_IRUSR, NULL, &proc_kpagetype_operations);
+#ifdef CONFIG_COMPACTION
+	proc_create("kpagecskip", S_IRUSR, NULL, &proc_kpagecskip_operations);
+#endif
 	return 0;
 }
 module_init(proc_page_init);

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