On Wed, Mar 16, 2016 at 08:31:14AM -0400, Brian Foster wrote:
> On Wed, Mar 16, 2016 at 05:18:04PM +0800, Zorro Lang wrote:
> > 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>
> > ---
>
> I'm a little curious why one would use this as opposed to 'mremap -m' in
> the context of xfs_io (it certainly might make sense for an
> application). It sounds like any xfstests tests, for example, that is
> susceptible to this problem might want to use -m even if -s is employed
> as well. Can you provide any additional context on this or do you have a
> use case in mind?
>
> That said, I'm not against adding this to the xfs_io toolbox and the
> code looks Ok to me:
Hi Brian,
I hit this problem when I try to use xfs_io to rewrite LTP's mmap16
testcase for xfstests(I know I can backport that mmap16.c into
xfstests/src directly, but I just try to use xfs_io). That case
from linux commit:
90a8020 vfs: fix data corruption when blocksize < pagesize for
mmaped data
For reproduce that bug, I think I shouldn't move page when mremap. So
I need mremap to extend mapped space from orignal starting address.
If no this option, xfs_io -c "mmap 0 1024" -c "mremap 8192" will
hit ENOMEM error nearly 100%, but if use this option, it nearly always
remap successfully(on my test machine). So I think it maybe helpful
in the future, if someone try to mremap without "-m" :)
Thanks,
Zorro
>
> Reviewed-by: Brian Foster <bfoster@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
>
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