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authorPavel Emelyanov <xemul@parallels.com>2013-07-03 15:01:22 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2013-07-03 16:07:26 -0700
commit541c237c0923f567c9c4cabb8a81635baadc713f (patch)
tree5f544cd43acff9e09c6f126f678e2d7c89920bbf /fs/proc
parent0f8975ec4db2c8b5bd111b211292ca9be0feb6b8 (diff)
pagemap: prepare to reuse constant bits with page-shift
In order to reuse bits from pagemap entries gracefully, we leave the entries as is but on pagemap open emit a warning in dmesg, that bits 55-60 are about to change in a couple of releases. Next, if a user issues soft-dirty clear command via the clear_refs file (it was disabled before v3.9) we assume that he's aware of the new pagemap format, note that fact and report the bits in pagemap in the new manner. The "migration strategy" looks like this then: 1. existing users are not affected -- they don't touch soft-dirty feature, thus see old bits in pagemap, but are warned and have time to fix themselves 2. those who use soft-dirty know about new pagemap format 3. some time soon we get rid of any signs of page-shift in pagemap as well as this trick with clear-soft-dirty affecting pagemap format. Signed-off-by: Pavel Emelyanov <xemul@parallels.com> Cc: Matt Mackall <mpm@selenic.com> Cc: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com> Cc: Glauber Costa <glommer@parallels.com> Cc: Marcelo Tosatti <mtosatti@redhat.com> Cc: KOSAKI Motohiro <kosaki.motohiro@gmail.com> Cc: Stephen Rothwell <sfr@canb.auug.org.au> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'fs/proc')
-rw-r--r--fs/proc/task_mmu.c35
1 files changed, 34 insertions, 1 deletions
diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index a18e065c1c3e..dbf61f6174f0 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -689,6 +689,23 @@ const struct file_operations proc_tid_smaps_operations = {
.release = seq_release_private,
};
+/*
+ * We do not want to have constant page-shift bits sitting in
+ * pagemap entries and are about to reuse them some time soon.
+ *
+ * Here's the "migration strategy":
+ * 1. when the system boots these bits remain what they are,
+ * but a warning about future change is printed in log;
+ * 2. once anyone clears soft-dirty bits via clear_refs file,
+ * these flag is set to denote, that user is aware of the
+ * new API and those page-shift bits change their meaning.
+ * The respective warning is printed in dmesg;
+ * 3. In a couple of releases we will remove all the mentions
+ * of page-shift in pagemap entries.
+ */
+
+static bool soft_dirty_cleared __read_mostly;
+
enum clear_refs_types {
CLEAR_REFS_ALL = 1,
CLEAR_REFS_ANON,
@@ -778,6 +795,13 @@ static ssize_t clear_refs_write(struct file *file, const char __user *buf,
type = (enum clear_refs_types)itype;
if (type < CLEAR_REFS_ALL || type >= CLEAR_REFS_LAST)
return -EINVAL;
+
+ if (type == CLEAR_REFS_SOFT_DIRTY) {
+ soft_dirty_cleared = true;
+ pr_warn_once("The pagemap bits 55-60 has changed their meaning! "
+ "See the linux/Documentation/vm/pagemap.txt for details.\n");
+ }
+
task = get_proc_task(file_inode(file));
if (!task)
return -ESRCH;
@@ -1091,7 +1115,7 @@ static ssize_t pagemap_read(struct file *file, char __user *buf,
if (!count)
goto out_task;
- pm.v2 = false;
+ pm.v2 = soft_dirty_cleared;
pm.len = PM_ENTRY_BYTES * (PAGEMAP_WALK_SIZE >> PAGE_SHIFT);
pm.buffer = kmalloc(pm.len, GFP_TEMPORARY);
ret = -ENOMEM;
@@ -1164,9 +1188,18 @@ out:
return ret;
}
+static int pagemap_open(struct inode *inode, struct file *file)
+{
+ pr_warn_once("Bits 55-60 of /proc/PID/pagemap entries are about "
+ "to stop being page-shift some time soon. See the "
+ "linux/Documentation/vm/pagemap.txt for details.\n");
+ return 0;
+}
+
const struct file_operations proc_pagemap_operations = {
.llseek = mem_lseek, /* borrow this */
.read = pagemap_read,
+ .open = pagemap_open,
};
#endif /* CONFIG_PROC_PAGE_MONITOR */