Re: [PATCH v10 6/7] nfs/localio: add tracepoints for misaligned DIO READ and WRITE support

[Mike Snitzer <snitzer@kernel.org>]

On Thu, Sep 18, 2025 at 03:55:32PM -0400, Anna Schumaker wrote:
> 
> 
> On 9/18/25 3:21 PM, Mike Snitzer wrote:
> > On Thu, Sep 18, 2025 at 01:55:03PM -0400, Anna Schumaker wrote:
> >>
> >>
> >> On 9/18/25 1:46 PM, Mike Snitzer wrote:
> >>> On Thu, Sep 18, 2025 at 01:33:30PM -0400, Anna Schumaker wrote:
> >>>> Hi Mike,
> >>>>
> >>>> On 9/17/25 2:18 PM, Mike Snitzer wrote:
> >>>>> Add nfs_local_dio_class and use it to create nfs_local_dio_read,
> >>>>> nfs_local_dio_write and nfs_local_dio_misaligned trace events.
> >>>>>
> >>>>> These trace events show how NFS LOCALIO splits a given misaligned
> >>>>> IO into a mix of misaligned head and/or tail extents and a DIO-aligned
> >>>>> middle extent.  The misaligned head and/or tail extents are issued
> >>>>> using buffered IO and the DIO-aligned middle is issued using O_DIRECT.
> >>>>>
> >>>>> This combination of trace events is useful for LOCALIO DIO READs:
> >>>>>
> >>>>>   echo 1 > /sys/kernel/tracing/events/nfs/nfs_local_dio_read/enable
> >>>>>   echo 1 > /sys/kernel/tracing/events/nfs/nfs_local_dio_misaligned/enable
> >>>>>   echo 1 > /sys/kernel/tracing/events/nfs/nfs_initiate_read/enable
> >>>>>   echo 1 > /sys/kernel/tracing/events/nfs/nfs_readpage_done/enable
> >>>>>   echo 1 > /sys/kernel/tracing/events/xfs/xfs_file_direct_read/enable
> >>>>>
> >>>>> This combination of trace events is useful for LOCALIO DIO WRITEs:
> >>>>>
> >>>>>   echo 1 > /sys/kernel/tracing/events/nfs/nfs_local_dio_write/enable
> >>>>>   echo 1 > /sys/kernel/tracing/events/nfs/nfs_local_dio_misaligned/enable
> >>>>>   echo 1 > /sys/kernel/tracing/events/nfs/nfs_initiate_write/enable
> >>>>>   echo 1 > /sys/kernel/tracing/events/nfs/nfs_writeback_done/enable
> >>>>>   echo 1 > /sys/kernel/tracing/events/xfs/xfs_file_direct_write/enable
> >>>>
> >>>> I'm having a lot of trouble compiling this patch. I'm seeing errors like this:
> >>>>
> >>>>
> >>>> fs/nfs/nfstrace.h:1800:1: error: declaration of 'struct nfs_local_dio' will not be visible outside of this function [-Werror,-Wvisibility]
> >>>>  1800 | DEFINE_NFS_LOCAL_DIO_EVENT(write);
> >>>>       | ^
> >>>> fs/nfs/nfstrace.h:1796:17: note: expanded from macro 'DEFINE_NFS_LOCAL_DIO_EVENT'
> >>>>  1796 |                  const struct nfs_local_dio *local_dio),\
> >>>>       |                               ^
> >>>> fs/nfs/nfstrace.h:1800:1: error: declaration of 'struct nfs_local_dio' will not be visible outside of this function [-Werror,-Wvisibility]
> >>>> fs/nfs/nfstrace.h:1796:17: note: expanded from macro 'DEFINE_NFS_LOCAL_DIO_EVENT'
> >>>>  1796 |                  const struct nfs_local_dio *local_dio),\
> >>>>       |                               ^
> >>>> fs/nfs/nfstrace.h:1800:1: error: declaration of 'struct nfs_local_dio' will not be visible outside of this function [-Werror,-Wvisibility]
> >>>> fs/nfs/nfstrace.h:1796:17: note: expanded from macro 'DEFINE_NFS_LOCAL_DIO_EVENT'
> >>>>  1796 |                  const struct nfs_local_dio *local_dio),\
> >>>>       |                               ^
> >>>> fs/nfs/nfstrace.h:1800:1: error: declaration of 'struct nfs_local_dio' will not be visible outside of this function [-Werror,-Wvisibility]
> >>>> fs/nfs/nfstrace.h:1796:17: note: expanded from macro 'DEFINE_NFS_LOCAL_DIO_EVENT'
> >>>>  1796 |                  const struct nfs_local_dio *local_dio),\
> >>>>       |                               ^
> >>>> fs/nfs/nfstrace.h:1800:1: error: declaration of 'struct nfs_local_dio' will not be visible outside of this function [-Werror,-Wvisibility]
> >>>> fs/nfs/nfstrace.h:1796:17: note: expanded from macro 'DEFINE_NFS_LOCAL_DIO_EVENT'
> >>>>  1796 |                  const struct nfs_local_dio *local_dio),\
> >>>>       |                               ^
> >>>> fs/nfs/nfstrace.h:1800:1: error: declaration of 'struct nfs_local_dio' will not be visible outside of this function [-Werror,-Wvisibility]
> >>>> fs/nfs/nfstrace.h:1796:17: note: expanded from macro 'DEFINE_NFS_LOCAL_DIO_EVENT'
> >>>>  1796 |                  const struct nfs_local_dio *local_dio),\
> >>>>       |                               ^
> >>>> fs/nfs/nfstrace.h:1800:1: error: declaration of 'struct nfs_local_dio' will not be visible outside of this function [-Werror,-Wvisibility]
> >>>> fs/nfs/nfstrace.h:1796:17: note: expanded from macro 'DEFINE_NFS_LOCAL_DIO_EVENT'
> >>>>  1796 |                  const struct nfs_local_dio *local_dio),\
> >>>>       |                               ^
> >>>> fs/nfs/nfstrace.h:1800:1: error: incompatible pointer types passing 'const struct nfs_local_dio *' to parameter of type 'const struct nfs_local_dio *' [-Werror,-Wincompatible-pointer-types]
> >>>>  1800 | DEFINE_NFS_LOCAL_DIO_EVENT(write);

BTW, this ^ last incompatible pointer type error doesn't make any
sense.

I'm concerned this is very specific to your development environment.

(more reply below)

> >>>>
> >>>>
> >>>> Am I missing a patch somewhere along the line?
> >>>>
> >>>> Thanks,
> >>>> Anna
> >>>>
> >>>>>
> >>>>> Signed-off-by: Mike Snitzer <snitzer@kernel.org>
> >>>>> ---
> >>>>>  fs/nfs/internal.h | 10 +++++++
> >>>>>  fs/nfs/localio.c  | 19 ++++++-------
> >>>>>  fs/nfs/nfs3xdr.c  |  2 +-
> >>>>>  fs/nfs/nfstrace.h | 70 +++++++++++++++++++++++++++++++++++++++++++++++
> >>>>>  4 files changed, 89 insertions(+), 12 deletions(-)
> >>>>>
> >>>>> diff --git a/fs/nfs/internal.h b/fs/nfs/internal.h
> >>>>> index d44233cfd7949..3d380c45b5ef3 100644
> >>>>> --- a/fs/nfs/internal.h
> >>>>> +++ b/fs/nfs/internal.h
> >>>>> @@ -456,6 +456,16 @@ extern int nfs_wait_bit_killable(struct wait_bit_key *key, int mode);
> >>>>>  
> >>>>>  #if IS_ENABLED(CONFIG_NFS_LOCALIO)
> >>>>>  /* localio.c */
> >>>>> +struct nfs_local_dio {
> >>>>> +	u32 mem_align;
> >>>>> +	u32 offset_align;
> >>>>> +	loff_t middle_offset;
> >>>>> +	loff_t end_offset;
> >>>>> +	ssize_t	start_len;	/* Length for misaligned first extent */
> >>>>> +	ssize_t	middle_len;	/* Length for DIO-aligned middle extent */
> >>>>> +	ssize_t	end_len;	/* Length for misaligned last extent */
> >>>>> +};
> >>>>> +
> >>>>>  extern void nfs_local_probe_async(struct nfs_client *);
> >>>>>  extern void nfs_local_probe_async_work(struct work_struct *);
> >>>>>  extern struct nfsd_file *nfs_local_open_fh(struct nfs_client *,
> >>>>> diff --git a/fs/nfs/localio.c b/fs/nfs/localio.c
> >>>>> index 768af570183af..cf1533759646e 100644
> >>>>> --- a/fs/nfs/localio.c
> >>>>> +++ b/fs/nfs/localio.c
> >>>>> @@ -322,16 +322,6 @@ nfs_local_iocb_alloc(struct nfs_pgio_header *hdr,
> >>>>>  	return iocb;
> >>>>>  }
> >>>>>  
> >>>>> -struct nfs_local_dio {
> >>>>> -	u32 mem_align;
> >>>>> -	u32 offset_align;
> >>>>> -	loff_t middle_offset;
> >>>>> -	loff_t end_offset;
> >>>>> -	ssize_t	start_len;	/* Length for misaligned first extent */
> >>>>> -	ssize_t	middle_len;	/* Length for DIO-aligned middle extent */
> >>>>> -	ssize_t	end_len;	/* Length for misaligned last extent */
> >>>>> -};
> >>>>> -
> >>>>>  static bool
> >>>>>  nfs_is_local_dio_possible(struct nfs_local_kiocb *iocb, int rw,
> >>>>>  			  size_t len, struct nfs_local_dio *local_dio)
> >>>>> @@ -367,6 +357,10 @@ nfs_is_local_dio_possible(struct nfs_local_kiocb *iocb, int rw,
> >>>>>  	local_dio->middle_len = middle_end - start_end;
> >>>>>  	local_dio->end_len = orig_end - middle_end;
> >>>>>  
> >>>>> +	if (rw == ITER_DEST)
> >>>>> +		trace_nfs_local_dio_read(hdr->inode, offset, len, local_dio);
> >>>>> +	else
> >>>>> +		trace_nfs_local_dio_write(hdr->inode, offset, len, local_dio);
> >>>>>  	return true;
> >>>>>  }
> >>>>>  
> >>>>> @@ -446,8 +440,11 @@ nfs_local_iters_setup_dio(struct nfs_local_kiocb *iocb, int rw,
> >>>>>  		nfs_iov_iter_aligned_bvec(&iters[n_iters],
> >>>>>  			local_dio->mem_align-1, local_dio->offset_align-1);
> >>>>>  
> >>>>> -	if (unlikely(!iocb->iter_is_dio_aligned[n_iters]))
> >>>>> +	if (unlikely(!iocb->iter_is_dio_aligned[n_iters])) {
> >>>>> +		trace_nfs_local_dio_misaligned(iocb->hdr->inode,
> >>>>> +			iocb->hdr->args.offset, len, local_dio);
> >>>>>  		return 0; /* no DIO-aligned IO possible */
> >>>>> +	}
> >>>>>  	++n_iters;
> >>>>>  
> >>>>>  	iocb->n_iters = n_iters;
> >>>>> diff --git a/fs/nfs/nfs3xdr.c b/fs/nfs/nfs3xdr.c
> >>>>> index 4ae01c10b7e28..e17d729084125 100644
> >>>>> --- a/fs/nfs/nfs3xdr.c
> >>>>> +++ b/fs/nfs/nfs3xdr.c
> >>>>> @@ -23,8 +23,8 @@
> >>>>>  #include <linux/nfsacl.h>
> >>>>>  #include <linux/nfs_common.h>
> >>>>>  
> >>>>> -#include "nfstrace.h"
> >>>>>  #include "internal.h"
> >>>>> +#include "nfstrace.h"
> >>>>>  
> >>>>>  #define NFSDBG_FACILITY		NFSDBG_XDR
> >>>>>  
> >>>
> >>> This change ^ was critical for fixing unknown type issues for 'struct
> >>> nfs_local_dio' issues on my build. But I haven't seen the issue you've
> >>> reported above. I'll try applying my changes on very latest upstream
> >>> tree.
> >>>
> >>> Which tree/branch are you using for your baseline?  Also, which
> >>> version of gcc (which distro even) are you using?
> >>
> >> I'm using my linux-next branch from: git.linux-nfs.org/projects/anna/linux-nfs.git.
> >> It's v6.17-rc6 plus the patches I'm planning for the next merge window.
> > 
> > Like I mentioned in another reply in this thread, I've pushed a tree
> > that is based on your linux-next branch here:
> > https://git.kernel.org/pub/scm/linux/kernel/git/snitzer/linux.git/log/?h=anna-linux-next-6.18
> > 
> > I've verified that this builds fine for me when using either:
> > EL8.10 with gcc 11.2.1-9
> > EL9.5 with 11.5.0-5
> > 
> > Which distro and gcc version are you using?
> 
> This is with Archlinux and clang v 20.1.8, although I do
> see similar errors with gcc 15.2.1.

OK, so way more bleeding edge than my 2 versions of gcc 11.x

I tried to see if disabling CONFIG_NFS_LOCALIO might explain it, but
that compiles fine for me too.

Please feel free to share your .config with me off-list and I'll keep
chasing.

Thanks,
Mike