This patch come from a test likes below:
xfs_io -t -f
-c "truncate 10000"
-c "mmap -rw 0 1024"
-c "mremap 8192"
file
mremap always hit ENOMEM error, when it try to remap more space
without MREMAP_MAYMOVE flag. This's a normal condition, due to
no free space after mapped 1024 bytes region.
But if we try to mremap from the original mapped starting point in
a C program, at first we always do:
addr = mmap(NULL, res_size, prot, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
munmap(addr, res_size);
Then do:
addr = mmap(addr, real_len, ...);
The "res_size" is bigger than "real_len". This will help us get a
region between real_len and res_size, which maybe free space. The
truth is we can't guarantee that this free memory will stay free.
But this method is still very helpful for reserve some free space
in short time.
After merge this patch, we can resolve above mremap problem by run:
xfs_io -t -f
...
-c "mmap -rw -s 8192 0 1024"
-c "mremap 8192"
...
Although we can't sure it's useful 100%, it really have pretty high
success rate.
Signed-off-by: Zorro Lang <zlang@xxxxxxxxxx>
---
io/mmap.c | 29 +++++++++++++++++++++++------
man/man8/xfs_io.8 | 17 ++++++++++++++++-
2 files changed, 39 insertions(+), 7 deletions(-)
diff --git a/io/mmap.c b/io/mmap.c
index 5970069..6cd37a9 100644
--- a/io/mmap.c
+++ b/io/mmap.c
@@ -146,6 +146,7 @@ mmap_help(void)
" -r -- map with PROT_READ protection\n"
" -w -- map with PROT_WRITE protection\n"
" -x -- map with PROT_EXEC protection\n"
+" -s <size> -- first do mmap(size)/munmap(size), try to reserve some free space\n"
" If no protection mode is specified, all are used by default.\n"
"\n"));
}
@@ -156,8 +157,8 @@ mmap_f(
char **argv)
{
off64_t offset;
- ssize_t length;
- void *address;
+ ssize_t length = 0, length2 = 0;
+ void *address = NULL;
char *filename;
size_t blocksize, sectsize;
int c, prot = 0;
@@ -181,7 +182,9 @@ mmap_f(
return 0;
}
- while ((c = getopt(argc, argv, "rwx")) != EOF) {
+ init_cvtnum(&blocksize, §size);
+
+ while ((c = getopt(argc, argv, "rwxs:")) != EOF) {
switch (c) {
case 'r':
prot |= PROT_READ;
@@ -192,6 +195,9 @@ mmap_f(
case 'x':
prot |= PROT_EXEC;
break;
+ case 's':
+ length2 = cvtnum(blocksize, sectsize, optarg);
+ break;
default:
return command_usage(&mmap_cmd);
}
@@ -202,7 +208,6 @@ mmap_f(
if (optind != argc - 2)
return command_usage(&mmap_cmd);
- init_cvtnum(&blocksize, §size);
offset = cvtnum(blocksize, sectsize, argv[optind]);
if (offset < 0) {
printf(_("non-numeric offset argument -- %s\n"), argv[optind]);
@@ -221,7 +226,19 @@ mmap_f(
return 0;
}
- address = mmap(NULL, length, prot, MAP_SHARED, file->fd, offset);
+ /*
+ * mmap and munmap memory area of length2 region is helpful to
+ * make a region of extendible free memory. It's generally used
+ * for later mremap operation(no MREMAP_MAYMOVE flag). But there
+ * isn't guarantee that the memory after length (up to length2)
+ * will stay free.
+ */
+ if (length2 > length) {
+ address = mmap(NULL, length2, prot,
+ MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+ munmap(address, length2);
+ }
+ address = mmap(address, length, prot, MAP_SHARED, file->fd, offset);
if (address == MAP_FAILED) {
perror("mmap");
free(filename);
@@ -647,7 +664,7 @@ mmap_init(void)
mmap_cmd.argmin = 0;
mmap_cmd.argmax = -1;
mmap_cmd.flags = CMD_NOMAP_OK | CMD_NOFILE_OK | CMD_FOREIGN_OK;
- mmap_cmd.args = _("[N] | [-rwx] [off len]");
+ mmap_cmd.args = _("[N] | [-rwx] [-s size] [off len]");
mmap_cmd.oneline =
_("mmap a range in the current file, show mappings");
mmap_cmd.help = mmap_help;
diff --git a/man/man8/xfs_io.8 b/man/man8/xfs_io.8
index 33fbe6a..93a8a00 100644
--- a/man/man8/xfs_io.8
+++ b/man/man8/xfs_io.8
@@ -559,7 +559,7 @@ Do not print timing statistics at all.
.SH MEMORY MAPPED I/O COMMANDS
.TP
-.BI "mmap [ " N " | [[ \-rwx ] " "offset length " ]]
+.BI "mmap [ " N " | [[ \-rwx ] [\-s " size " ] " "offset length " ]]
With no arguments,
.B mmap
shows the current mappings. Specifying a single numeric argument
@@ -575,6 +575,21 @@ PROT_WRITE
.RB ( \-w ),
and PROT_EXEC
.RB ( \-x ).
+.BI \-s " size"
+is used to do a mmap(size) && munmap(size) operation at first, try to reserve some
+extendible free memory space, if
+.I size
+is bigger than
+.I length
+parameter. But there's not guarantee that the memory after
+.I length
+( up to
+.I size
+) will stay free.
+.B e.g.
+"mmap -rw -s 8192 1024" will mmap 0 ~ 1024 bytes memory, but try to reserve 1024 ~ 8192
+free space(no guarantee). This free space will helpful for "mremap 8192" without
+MREMAP_MAYMOVE flag.
.TP
.B mm
See the
--
2.5.0
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