Re: [PATCH v2 3/6] dax: add tracepoint infrastructure, PMD tracing

From: Jan Kara
Date: Thu Dec 01 2016 - 03:10:40 EST

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On Wed 30-11-16 16:45:30, Ross Zwisler wrote:
> Tracepoints are the standard way to capture debugging and tracing
> information in many parts of the kernel, including the XFS and ext4
> filesystems. Create a tracepoint header for FS DAX and add the first DAX
> tracepoints to the PMD fault handler. This allows the tracing for DAX to
> be done in the same way as the filesystem tracing so that developers can
> look at them together and get a coherent idea of what the system is doing.
>
> I added both an entry and exit tracepoint because future patches will add
> tracepoints to child functions of dax_iomap_pmd_fault() like
> dax_pmd_load_hole() and dax_pmd_insert_mapping(). We want those messages to
> be wrapped by the parent function tracepoints so the code flow is more
> easily understood. Having entry and exit tracepoints for faults also
> allows us to easily see what filesystems functions were called during the
> fault. These filesystem functions get executed via iomap_begin() and
> iomap_end() calls, for example, and will have their own tracepoints.
>
> For PMD faults we primarily want to understand the type of mapping, the
> fault flags, the faulting address and whether it fell back to 4k faults.
> If it fell back to 4k faults the tracepoints should let us understand why.
>
> I named the new tracepoint header file "fs_dax.h" to allow for device DAX
> to have its own separate tracing header in the same directory at some
> point.
>
> Here is an example output for these events from a successful PMD fault:
>
> big-1441 [005] .... 32.582758: xfs_filemap_pmd_fault: dev 259:0 ino
> 0x1003
>
> big-1441 [005] .... 32.582776: dax_pmd_fault: dev 259:0 ino 0x1003
> shared WRITE|ALLOW_RETRY|KILLABLE|USER address 0x10505000 vm_start
> 0x10200000 vm_end 0x10700000 pgoff 0x200 max_pgoff 0x1400
>
> big-1441 [005] .... 32.583292: dax_pmd_fault_done: dev 259:0 ino 0x1003
> shared WRITE|ALLOW_RETRY|KILLABLE|USER address 0x10505000 vm_start
> 0x10200000 vm_end 0x10700000 pgoff 0x200 max_pgoff 0x1400 NOPAGE
>
> Signed-off-by: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx>
> Suggested-by: Dave Chinner <david@xxxxxxxxxxxxx>

Looks good. You can add:

Reviewed-by: Jan Kara <jack@xxxxxxx>

Honza

> ---
> fs/dax.c | 30 ++++++++++++-------
> include/linux/mm.h | 25 ++++++++++++++++
> include/trace/events/fs_dax.h | 68 +++++++++++++++++++++++++++++++++++++++++++
> 3 files changed, 113 insertions(+), 10 deletions(-)
> create mode 100644 include/trace/events/fs_dax.h
>
> diff --git a/fs/dax.c b/fs/dax.c
> index b14335c..4a99c2e 100644
> --- a/fs/dax.c
> +++ b/fs/dax.c
> @@ -35,6 +35,9 @@
> #include <linux/iomap.h>
> #include "internal.h"
>
> +#define CREATE_TRACE_POINTS
> +#include <trace/events/fs_dax.h>
> +
> /* We choose 4096 entries - same as per-zone page wait tables */
> #define DAX_WAIT_TABLE_BITS 12
> #define DAX_WAIT_TABLE_ENTRIES (1 << DAX_WAIT_TABLE_BITS)
> @@ -1311,6 +1314,16 @@ int dax_iomap_pmd_fault(struct vm_area_struct *vma, unsigned long address,
> loff_t pos;
> int error;
>
> + /*
> + * Check whether offset isn't beyond end of file now. Caller is
> + * supposed to hold locks serializing us with truncate / punch hole so
> + * this is a reliable test.
> + */
> + pgoff = linear_page_index(vma, pmd_addr);
> + max_pgoff = (i_size_read(inode) - 1) >> PAGE_SHIFT;
> +
> + trace_dax_pmd_fault(inode, vma, address, flags, pgoff, max_pgoff, 0);
> +
> /* Fall back to PTEs if we're going to COW */
> if (write && !(vma->vm_flags & VM_SHARED))
> goto fallback;
> @@ -1321,16 +1334,10 @@ int dax_iomap_pmd_fault(struct vm_area_struct *vma, unsigned long address,
> if ((pmd_addr + PMD_SIZE) > vma->vm_end)
> goto fallback;
>
> - /*
> - * Check whether offset isn't beyond end of file now. Caller is
> - * supposed to hold locks serializing us with truncate / punch hole so
> - * this is a reliable test.
> - */
> - pgoff = linear_page_index(vma, pmd_addr);
> - max_pgoff = (i_size_read(inode) - 1) >> PAGE_SHIFT;
> -
> - if (pgoff > max_pgoff)
> - return VM_FAULT_SIGBUS;
> + if (pgoff > max_pgoff) {
> + result = VM_FAULT_SIGBUS;
> + goto out;
> + }
>
> /* If the PMD would extend beyond the file size */
> if ((pgoff | PG_PMD_COLOUR) > max_pgoff)
> @@ -1401,6 +1408,9 @@ int dax_iomap_pmd_fault(struct vm_area_struct *vma, unsigned long address,
> split_huge_pmd(vma, pmd, address);
> count_vm_event(THP_FAULT_FALLBACK);
> }
> +out:
> + trace_dax_pmd_fault_done(inode, vma, address, flags, pgoff, max_pgoff,
> + result);
> return result;
> }
> EXPORT_SYMBOL_GPL(dax_iomap_pmd_fault);
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index a5f52c0..30f416a 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -281,6 +281,17 @@ extern pgprot_t protection_map[16];
> #define FAULT_FLAG_REMOTE 0x80 /* faulting for non current tsk/mm */
> #define FAULT_FLAG_INSTRUCTION 0x100 /* The fault was during an instruction fetch */
>
> +#define FAULT_FLAG_TRACE \
> + { FAULT_FLAG_WRITE, "WRITE" }, \
> + { FAULT_FLAG_MKWRITE, "MKWRITE" }, \
> + { FAULT_FLAG_ALLOW_RETRY, "ALLOW_RETRY" }, \
> + { FAULT_FLAG_RETRY_NOWAIT, "RETRY_NOWAIT" }, \
> + { FAULT_FLAG_KILLABLE, "KILLABLE" }, \
> + { FAULT_FLAG_TRIED, "TRIED" }, \
> + { FAULT_FLAG_USER, "USER" }, \
> + { FAULT_FLAG_REMOTE, "REMOTE" }, \
> + { FAULT_FLAG_INSTRUCTION, "INSTRUCTION" }
> +
> /*
> * vm_fault is filled by the the pagefault handler and passed to the vma's
> * ->fault function. The vma's ->fault is responsible for returning a bitmask
> @@ -1107,6 +1118,20 @@ static inline void clear_page_pfmemalloc(struct page *page)
> VM_FAULT_HWPOISON | VM_FAULT_HWPOISON_LARGE | \
> VM_FAULT_FALLBACK)
>
> +#define VM_FAULT_RESULT_TRACE \
> + { VM_FAULT_OOM, "OOM" }, \
> + { VM_FAULT_SIGBUS, "SIGBUS" }, \
> + { VM_FAULT_MAJOR, "MAJOR" }, \
> + { VM_FAULT_WRITE, "WRITE" }, \
> + { VM_FAULT_HWPOISON, "HWPOISON" }, \
> + { VM_FAULT_HWPOISON_LARGE, "HWPOISON_LARGE" }, \
> + { VM_FAULT_SIGSEGV, "SIGSEGV" }, \
> + { VM_FAULT_NOPAGE, "NOPAGE" }, \
> + { VM_FAULT_LOCKED, "LOCKED" }, \
> + { VM_FAULT_RETRY, "RETRY" }, \
> + { VM_FAULT_FALLBACK, "FALLBACK" }, \
> + { VM_FAULT_DONE_COW, "DONE_COW" }
> +
> /* Encode hstate index for a hwpoisoned large page */
> #define VM_FAULT_SET_HINDEX(x) ((x) << 12)
> #define VM_FAULT_GET_HINDEX(x) (((x) >> 12) & 0xf)
> diff --git a/include/trace/events/fs_dax.h b/include/trace/events/fs_dax.h
> new file mode 100644
> index 0000000..5acc016
> --- /dev/null
> +++ b/include/trace/events/fs_dax.h
> @@ -0,0 +1,68 @@
> +#undef TRACE_SYSTEM
> +#define TRACE_SYSTEM fs_dax
> +
> +#if !defined(_TRACE_FS_DAX_H) || defined(TRACE_HEADER_MULTI_READ)
> +#define _TRACE_FS_DAX_H
> +
> +#include <linux/tracepoint.h>
> +
> +DECLARE_EVENT_CLASS(dax_pmd_fault_class,
> + TP_PROTO(struct inode *inode, struct vm_area_struct *vma,
> + unsigned long address, unsigned int flags, pgoff_t pgoff,
> + pgoff_t max_pgoff, int result),
> + TP_ARGS(inode, vma, address, flags, pgoff, max_pgoff, result),
> + TP_STRUCT__entry(
> + __field(dev_t, dev)
> + __field(unsigned long, ino)
> + __field(unsigned long, vm_start)
> + __field(unsigned long, vm_end)
> + __field(unsigned long, vm_flags)
> + __field(unsigned long, address)
> + __field(unsigned int, flags)
> + __field(pgoff_t, pgoff)
> + __field(pgoff_t, max_pgoff)
> + __field(int, result)
> + ),
> + TP_fast_assign(
> + __entry->dev = inode->i_sb->s_dev;
> + __entry->ino = inode->i_ino;
> + __entry->vm_start = vma->vm_start;
> + __entry->vm_end = vma->vm_end;
> + __entry->vm_flags = vma->vm_flags;
> + __entry->address = address;
> + __entry->flags = flags;
> + __entry->pgoff = pgoff;
> + __entry->max_pgoff = max_pgoff;
> + __entry->result = result;
> + ),
> + TP_printk("dev %d:%d ino %#lx %s %s address %#lx vm_start "
> + "%#lx vm_end %#lx pgoff %#lx max_pgoff %#lx %s",
> + MAJOR(__entry->dev),
> + MINOR(__entry->dev),
> + __entry->ino,
> + __entry->vm_flags & VM_SHARED ? "shared" : "private",
> + __print_flags(__entry->flags, "|", FAULT_FLAG_TRACE),
> + __entry->address,
> + __entry->vm_start,
> + __entry->vm_end,
> + __entry->pgoff,
> + __entry->max_pgoff,
> + __print_flags(__entry->result, "|", VM_FAULT_RESULT_TRACE)
> + )
> +)
> +
> +#define DEFINE_PMD_FAULT_EVENT(name) \
> +DEFINE_EVENT(dax_pmd_fault_class, name, \
> + TP_PROTO(struct inode *inode, struct vm_area_struct *vma, \
> + unsigned long address, unsigned int flags, pgoff_t pgoff, \
> + pgoff_t max_pgoff, int result), \
> + TP_ARGS(inode, vma, address, flags, pgoff, max_pgoff, result))
> +
> +DEFINE_PMD_FAULT_EVENT(dax_pmd_fault);
> +DEFINE_PMD_FAULT_EVENT(dax_pmd_fault_done);
> +
> +
> +#endif /* _TRACE_FS_DAX_H */
> +
> +/* This part must be outside protection */
> +#include <trace/define_trace.h>
> --
> 2.7.4
>
--
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR

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