Thoughts on TMPFS no longer being considered "highly
experimental"
Peter Holm
peter at holm.cc
Fri Jun 24 13:21:08 UTC 2011
On Fri, Jun 24, 2011 at 02:06:27PM +0300, Kostik Belousov wrote:
> On Fri, Jun 24, 2011 at 12:30:16PM +0200, Peter Holm wrote:
> > On Thu, Jun 23, 2011 at 11:21:53PM +0300, Kostik Belousov wrote:
> > > On Thu, Jun 23, 2011 at 09:31:09AM -0700, David O'Brien wrote:
> > > > Does anyone object to this patch?
> > > >
> > > > David Wolfskill and I have run TMPFS on a number of machines for two
> > > > years with no problems.
> > > >
> > > > I may have missed something, but I'm not aware of any serious PRs on
> > > > TMPFS either.
> > > >
> > > >
> > > > Index: tmpfs_vfsops.c
> > > > ===================================================================
> > > > --- tmpfs_vfsops.c (revision 221113)
> > > > +++ tmpfs_vfsops.c (working copy)
> > > > @@ -155,9 +155,6 @@ tmpfs_mount(struct mount *mp)
> > > > return EOPNOTSUPP;
> > > > }
> > > >
> > > > - printf("WARNING: TMPFS is considered to be a highly experimental "
> > > > - "feature in FreeBSD.\n");
> > > > -
> > > > vn_lock(mp->mnt_vnodecovered, LK_SHARED | LK_RETRY);
> > > > error = VOP_GETATTR(mp->mnt_vnodecovered, &va, mp->mnt_cred);
> > > > VOP_UNLOCK(mp->mnt_vnodecovered, 0);
> > >
> > > The things I am aware of:
> > > - there is a races on the lookup. They were papered over in r212305,
> > > but the bug was not really fixed, AFAIR.
> > >
> > > - the tmpfs does double-buffering for the mapped vnodes. This is quite
> > > insulting for the memory-backed fs, isn't it ? I have a patch, but it is
> > > still under review.
> > >
> > > - I believe Peter Holm has more test cases that fails with tmpfs. He
> > > would have more details. I somewhat remember some panic on execve(2) the
> > > binary located on tmpfs.
> > >
> >
> > I ran the TMPFS tests I have and so far I only spotted the mmap(2)
> > problem:
> >
> > http://people.freebsd.org/~pho/stress/log/tmpfs/
> It would be indeed good if the issue was the only remaining problem.
Well, more testing is needed for sure.
> The deadlock in tmpfs6.txt is caused by doing copyin() while having
> a page busied. This should be fixed indirectly by the patch to
> avoid double-buffering, I uploaded the latest version at
> http://people.freebsd.org/~kib/misc/tmpfs.5.patch
>
> >
> > > Removing the warning will not make the issues coming away.
> >
This doesn't compile:
===> tmpfs (all)
cc -O2 -pipe -fno-strict-aliasing -Werror -D_KERNEL -DKLD_MODULE -nostdinc -DHAVE_KERNEL_OPTION_HEADERS -include /usr/src/sys/i386/compile/PHO/opt_global.h -I. -I@ -I@/contrib/altq
-finline-limit=8000 --param inline-unit-growth=100 --param large-function-growth=1000 -fno-common -g -I/usr/src/sys/i386/compile/PHO -mno-align-long-strings -mpreferred-stack-boundary=2 -mno-sse
-mno-mmx -msoft-float -ffreestanding -fstack-protector -std=iso9899:1999 -fstack-protector -Wall -Wredundant-decls -Wnested-externs -Wstrict-prototypes -Wmissing-prototypes -Wpointer-arith -Winline
-Wcast-qual -Wundef -Wno-pointer-sign -fformat-extensions -Wmissing-include-dirs -fdiagnostics-show-option -c /usr/src/sys/modules/tmpfs/../../fs/tmpfs/tmpfs_subr.c
cc1: warnings being treated as errors
/usr/src/sys/modules/tmpfs/../../fs/tmpfs/tmpfs_subr.c: In function 'tmpfs_reg_resize':
/usr/src/sys/modules/tmpfs/../../fs/tmpfs/tmpfs_subr.c:911: warning: 'uobj' is used uninitialized in this function
*** Error code 1
886 int
887 tmpfs_reg_resize(struct vnode *vp, off_t newsize)
888 {
889 struct tmpfs_mount *tmp;
890 struct tmpfs_node *node;
891 vm_object_t uobj;
892 vm_page_t m;
893 vm_pindex_t newpages, oldpages;
894 off_t oldsize;
895 size_t zerolen;
896
897 MPASS(vp->v_type == VREG);
898 MPASS(newsize >= 0);
899
900 node = VP_TO_TMPFS_NODE(vp);
901 tmp = VFS_TO_TMPFS(vp->v_mount);
902
903 /*
904 * Convert the old and new sizes to the number of pages needed to
905 * store them. It may happen that we do not need to do anything
906 * because the last allocated page can accommodate the change on
907 * its own.
908 */
909 oldsize = node->tn_size;
910 oldpages = OFF_TO_IDX(oldsize + PAGE_MASK);
911 MPASS(oldpages == uobj->size);
912 newpages = OFF_TO_IDX(newsize + PAGE_MASK);
913 if (newpages > oldpages &&
914 newpages - oldpages > TMPFS_PAGES_AVAIL(tmp))
915 return (ENOSPC);
916
917 TMPFS_LOCK(tmp);
918 tmp->tm_pages_used += (newpages - oldpages);
919 TMPFS_UNLOCK(tmp);
920
921 node->tn_size = newsize;
922 VM_OBJECT_LOCK(uobj);
- Peter
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