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-rw-r--r--Documentation/vm/pagemap.txt3
-rw-r--r--fs/proc/task_mmu.c35
2 files changed, 36 insertions, 2 deletions
diff --git a/Documentation/vm/pagemap.txt b/Documentation/vm/pagemap.txt
index 7587493c67f1..fd7c3cfddd8e 100644
--- a/Documentation/vm/pagemap.txt
+++ b/Documentation/vm/pagemap.txt
@@ -15,7 +15,8 @@ There are three components to pagemap:
* Bits 0-54 page frame number (PFN) if present
* Bits 0-4 swap type if swapped
* Bits 5-54 swap offset if swapped
- * Bits 55-60 page shift (page size = 1<<page shift)
+ * Bit 55 pte is soft-dirty (see Documentation/vm/soft-dirty.txt)
+ * Bits 56-60 zero
* Bit 61 page is file-page or shared-anon
* Bit 62 page swapped
* Bit 63 page present
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 */