[PATCH 0/1] NFS: Fix read_bytes for buffered reads

[PATCH 0/1] NFS: Fix read_bytes for buffered reads

[Dave Wysochanski]

This patch fixes the read_bytes count for NFS buffered reads.
Simple reproducer follows.

Before this patch:
# mount 127.0.0.1:/ /mnt/nfs
# bash
# function dump_stats { cat /proc/$$/io; }
# trap dump_stats EXIT
# cat /mnt/nfs/file1.bin > /dev/null
# exit
exit
rchar: 3587436
wchar: 1054077
syscr: 544
syscw: 33
read_bytes: 0
write_bytes: 0
cancelled_write_bytes: 0


After this patch:
# mount 127.0.0.1:/ /mnt/nfs
# bash
# function dump_stats { cat /proc/$$/io; }
# trap dump_stats EXIT
# cat /mnt/nfs/file1.bin > /dev/null
# exit
exit
rchar: 3587278
wchar: 1054161
syscr: 544
syscw: 33
read_bytes: 1048576
write_bytes: 0
cancelled_write_bytes: 0


Dave Wysochanski (1):
  NFS: Fix /proc/PID/io read_bytes for buffered reads

 fs/nfs/read.c | 3 +++
 1 file changed, 3 insertions(+)

-- 
2.31.1

[PATCH 1/1] NFS: Fix /proc/PID/io read_bytes for buffered reads

[Dave Wysochanski]

Prior to commit 8786fde8421c ("Convert NFS from readpages to
readahead"), nfs_readpages() used the old mm interface read_cache_pages()
which called task_io_account_read() for each NFS page read.  After
this commit, nfs_readpages() is converted to nfs_readahead(), which
now uses the new mm interface readahead_page().  The new interface
requires callers to call task_io_account_read() themselves.
In addition, to nfs_readahead() task_io_account_read() should also
be called from nfs_read_folio().

Fixes: 8786fde8421c ("Convert NFS from readpages to readahead")
Link: https://lore.kernel.org/linux-nfs/CAPt2mGNEYUk5u8V4abe=5MM5msZqmvzCVrtCP4Qw1n=gCHCnww@mail.gmail.com/
Signed-off-by: Dave Wysochanski <dwysocha@redhat.com>
---
 fs/nfs/read.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/fs/nfs/read.c b/fs/nfs/read.c
index c380cff4108e..e90988591df4 100644
--- a/fs/nfs/read.c
+++ b/fs/nfs/read.c
@@ -15,6 +15,7 @@
 #include <linux/stat.h>
 #include <linux/mm.h>
 #include <linux/slab.h>
+#include <linux/task_io_accounting_ops.h>
 #include <linux/pagemap.h>
 #include <linux/sunrpc/clnt.h>
 #include <linux/nfs_fs.h>
@@ -337,6 +338,7 @@ int nfs_read_folio(struct file *file, struct folio *folio)
 
 	trace_nfs_aop_readpage(inode, folio);
 	nfs_inc_stats(inode, NFSIOS_VFSREADPAGE);
+	task_io_account_read(folio_size(folio));
 
 	/*
 	 * Try to flush any pending writes to the file..
@@ -393,6 +395,7 @@ void nfs_readahead(struct readahead_control *ractl)
 
 	trace_nfs_aop_readahead(inode, readahead_pos(ractl), nr_pages);
 	nfs_inc_stats(inode, NFSIOS_VFSREADPAGES);
+	task_io_account_read(readahead_length(ractl));
 
 	ret = -ESTALE;
 	if (NFS_STALE(inode))
-- 
2.31.1

Re: [PATCH 1/1] NFS: Fix /proc/PID/io read_bytes for buffered reads

[Daire Byrne]

Thanks Dave.

I can confirm that this does indeed fix the reporting of
/proc/PID/read_bytes for us. I actually applied it (cleanly) to our
v5.18 based kernel as we use that in production on our render farm.

We use the read_bytes in our post render statistics to help track per render IO.

Tested-by: Daire Byrne <daire@dneg.com>


On Thu, 9 Mar 2023 at 19:00, Dave Wysochanski <dwysocha@redhat.com> wrote:
>
> Prior to commit 8786fde8421c ("Convert NFS from readpages to
> readahead"), nfs_readpages() used the old mm interface read_cache_pages()
> which called task_io_account_read() for each NFS page read.  After
> this commit, nfs_readpages() is converted to nfs_readahead(), which
> now uses the new mm interface readahead_page().  The new interface
> requires callers to call task_io_account_read() themselves.
> In addition, to nfs_readahead() task_io_account_read() should also
> be called from nfs_read_folio().
>
> Fixes: 8786fde8421c ("Convert NFS from readpages to readahead")
> Link: https://lore.kernel.org/linux-nfs/CAPt2mGNEYUk5u8V4abe=5MM5msZqmvzCVrtCP4Qw1n=gCHCnww@mail.gmail.com/
> Signed-off-by: Dave Wysochanski <dwysocha@redhat.com>
> ---
>  fs/nfs/read.c | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/fs/nfs/read.c b/fs/nfs/read.c
> index c380cff4108e..e90988591df4 100644
> --- a/fs/nfs/read.c
> +++ b/fs/nfs/read.c
> @@ -15,6 +15,7 @@
>  #include <linux/stat.h>
>  #include <linux/mm.h>
>  #include <linux/slab.h>
> +#include <linux/task_io_accounting_ops.h>
>  #include <linux/pagemap.h>
>  #include <linux/sunrpc/clnt.h>
>  #include <linux/nfs_fs.h>
> @@ -337,6 +338,7 @@ int nfs_read_folio(struct file *file, struct folio *folio)
>
>         trace_nfs_aop_readpage(inode, folio);
>         nfs_inc_stats(inode, NFSIOS_VFSREADPAGE);
> +       task_io_account_read(folio_size(folio));
>
>         /*
>          * Try to flush any pending writes to the file..
> @@ -393,6 +395,7 @@ void nfs_readahead(struct readahead_control *ractl)
>
>         trace_nfs_aop_readahead(inode, readahead_pos(ractl), nr_pages);
>         nfs_inc_stats(inode, NFSIOS_VFSREADPAGES);
> +       task_io_account_read(readahead_length(ractl));
>
>         ret = -ESTALE;
>         if (NFS_STALE(inode))
> --
> 2.31.1
>