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Message-ID: <51B79C85.7000800@windriver.com>
Date: Tue, 11 Jun 2013 17:54:13 -0400
From: Paul Gortmaker <paul.gortmaker@...driver.com>
To: "Theodore Ts'o" <tytso@....edu>
CC: <linux-ext4@...r.kernel.org>, <linux-rt-users@...r.kernel.org>
Subject: Re: [PATCH 1/4] jbd2/journal_commit_transaction: relocate state lock
to incorporate all users
On 13-06-11 02:48 PM, Paul Gortmaker wrote:
> [Re: [PATCH 1/4] jbd2/journal_commit_transaction: relocate state lock to incorporate all users] On 11/06/2013 (Tue 13:53) Theodore Ts'o wrote:
>
>> On Tue, Jun 11, 2013 at 01:38:24PM -0400, Paul Gortmaker wrote:
>>>
>>> +#if defined(CONFIG_JBD_DEBUG) || defined(CONFIG_JBD2_DEBUG)
>>> +static inline void __jbd_debug(int level, const char *file, const char *func,
>>> + unsigned int line, const char *fmt, ...)
>>> +{
>>> + struct va_format vaf;
>>> + va_list args;
>>> +
>>> + if (level > JOURNAL_ENABLE_DEBUG)
>>> + return;
>>> + va_start(args, fmt);
>>> + vaf.fmt = fmt;
>>> + vaf.va = &args;
>>> + printk(KERN_DEBUG "%s: (%s, %u): %pV\n", file, func, line, &vaf);
>>> + va_end(args);
>>> +}
>>> +#endif
>>
>> What's the difference in the overall size of jbd.ko and jbd2.ko using
>> an inline __jbd_debug compared with one where the __jbd_debug is
>> defined as a function in fs/jbd2/journal.c (or fs/jbd/journal.c; that
>> will be the problem trying to solve this problem for jbd and jbd2 at
>> the same time)?
>>
>> If gcc was competent at optimizing inline functions with varargs, this
>> might be fine. But I'm a bit concerned whether this might cause a lot
>> of bloat if CONFIG_JBD2_DEBUG is enabled. It would be nice if the
>> impact was small enough that people were willing to enable so it's
>> available when we want to do debuggin.
>
> There is a small delta for inline vs non-inline, but it isn't anywhere
> near as big as the off-vs-on delta (with gcc-4.7.3):
>
> JBD[2]_DEBUG off:
> text data bss dec hex filename
> 48072 113 128 48313 bcb9 fs/jbd2/built-in.o
> 36862 50 32 36944 9050 fs/jbd/built-in.o
>
> JBD[2]_DEBUG on, __jbd[2]_debug as two independent real void functions:
> text data bss dec hex filename
> 55261 115 132 55508 d8d4 fs/jbd2/built-in.o
> 43752 51 52 43855 ab4f fs/jbd/built-in.o
>
> JBD[2]_DEBUG on, __jbd_debug as a shared inline function in jbd_common.h:
> text data bss dec hex filename
> 55862 115 132 56109 db2d fs/jbd2/built-in.o
> 44353 51 52 44456 ada8 fs/jbd/built-in.o
>
> So it looks like you can choose whichever solution you like
> better. I don't have a real preference either way. The
The more I think about this, the more I'm inclined to go with
the two independent real void functions. It gives smaller code
(albeit only slightly) and it probably is a tiny amount easier
to read vs. trying to be clever to share ~20 lines of code.
Plus I can then separate the ext3 content from the ext4 content
and create appropriate CC (i.e. add Jan Kara) for those parts.
Paul.
--
> non-inline version looks like what I've included below.
>
> Paul.
> --
>
> From d22a2bbe9108934ba3d1374f61f6e3a01aaa36e6 Mon Sep 17 00:00:00 2001
> From: Paul Gortmaker <paul.gortmaker@...driver.com>
> Date: Tue, 11 Jun 2013 11:46:10 -0400
> Subject: [PATCH] jbd/jbd2: make jbd_debug that won't split printk statements
>
> Since the jbd_debug() is implemented with two separate printk()
> calls, it can lead to corrupted and misleading debug output like
> the following (see lines marked with "*"):
>
> [ 290.339362] (fs/jbd2/journal.c, 203): kjournald2: kjournald2 wakes
> [ 290.339365] (fs/jbd2/journal.c, 155): kjournald2: commit_sequence=42103, commit_request=42104
> [ 290.339369] (fs/jbd2/journal.c, 158): kjournald2: OK, requests differ
> [* 290.339376] (fs/jbd2/journal.c, 648): jbd2_log_wait_commit:
> [* 290.339379] (fs/jbd2/commit.c, 370): jbd2_journal_commit_transaction: JBD2: want 42104, j_commit_sequence=42103
> [* 290.339382] JBD2: starting commit of transaction 42104
> [ 290.339410] (fs/jbd2/revoke.c, 566): jbd2_journal_write_revoke_records: Wrote 0 revoke records
> [ 290.376555] (fs/jbd2/commit.c, 1088): jbd2_journal_commit_transaction: JBD2: commit 42104 complete, head 42079
>
> i.e. the debug output from log_wait_commit and journal_commit_transaction
> have become interleaved. The output should have been:
>
> (fs/jbd2/journal.c, 648): jbd2_log_wait_commit: JBD2: want 42104, j_commit_sequence=42103
> (fs/jbd2/commit.c, 370): jbd2_journal_commit_transaction: JBD2: starting commit of transaction 42104
>
> It is expected that this is not easy to replicate -- I was only able
> to cause it on preempt-rt kernels, and even then only under heavy
> I/O load. Ted suggested we make use of va_args to reduce it to a single
> printk() call to fix it.
>
> This was originally seen on ext4, but since ext3 should suffer the
> same problem, I've taken the next step to implement the same kind of
> fix there as well.
>
> Signed-off-by: Paul Gortmaker <paul.gortmaker@...driver.com>
>
> diff --git a/fs/jbd/journal.c b/fs/jbd/journal.c
> index 6510d63..5e046a6 100644
> --- a/fs/jbd/journal.c
> +++ b/fs/jbd/journal.c
> @@ -90,6 +90,23 @@ static int journal_convert_superblock_v1(journal_t *, journal_superblock_t *);
> static void __journal_abort_soft (journal_t *journal, int errno);
> static const char *journal_dev_name(journal_t *journal, char *buffer);
>
> +#ifdef CONFIG_JBD_DEBUG
> +void __jbd_debug(int level, const char *file, const char *func,
> + unsigned int line, const char *fmt, ...)
> +{
> + struct va_format vaf;
> + va_list args;
> +
> + if (level > journal_enable_debug)
> + return;
> + va_start(args, fmt);
> + vaf.fmt = fmt;
> + vaf.va = &args;
> + printk(KERN_DEBUG "%s: (%s, %u): %pV\n", file, func, line, &vaf);
> + va_end(args);
> +}
> +#endif
> +
> /*
> * Helper function used to manage commit timeouts
> */
> diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c
> index 9545757..6aa196e 100644
> --- a/fs/jbd2/journal.c
> +++ b/fs/jbd2/journal.c
> @@ -103,6 +103,23 @@ EXPORT_SYMBOL(jbd2_inode_cache);
> static void __journal_abort_soft (journal_t *journal, int errno);
> static int jbd2_journal_create_slab(size_t slab_size);
>
> +#ifdef CONFIG_JBD2_DEBUG
> +void __jbd2_debug(int level, const char *file, const char *func,
> + unsigned int line, const char *fmt, ...)
> +{
> + struct va_format vaf;
> + va_list args;
> +
> + if (level > jbd2_journal_enable_debug)
> + return;
> + va_start(args, fmt);
> + vaf.fmt = fmt;
> + vaf.va = &args;
> + printk(KERN_DEBUG "%s: (%s, %u): %pV\n", file, func, line, &vaf);
> + va_end(args);
> +}
> +#endif
> +
> /* Checksumming functions */
> int jbd2_verify_csum_type(journal_t *j, journal_superblock_t *sb)
> {
> diff --git a/include/linux/jbd.h b/include/linux/jbd.h
> index 6e5524f..bc12abc 100644
> --- a/include/linux/jbd.h
> +++ b/include/linux/jbd.h
> @@ -56,17 +56,13 @@
> */
> #define JBD_EXPENSIVE_CHECKING
> extern u8 journal_enable_debug;
> +void __jbd_debug(int level, const char *file, const char *func,
> + unsigned int line, const char *fmt, ...);
>
> -#define jbd_debug(n, f, a...) \
> - do { \
> - if ((n) <= journal_enable_debug) { \
> - printk (KERN_DEBUG "(%s, %d): %s: ", \
> - __FILE__, __LINE__, __func__); \
> - printk (f, ## a); \
> - } \
> - } while (0)
> +#define jbd_debug(n, fmt, a...) \
> + __jbd_debug((n), __FILE__, __func__, __LINE__, (fmt), ##a)
> #else
> -#define jbd_debug(f, a...) /**/
> +#define jbd_debug(n, fmt, a...) /**/
> #endif
>
> static inline void *jbd_alloc(size_t size, gfp_t flags)
> diff --git a/include/linux/jbd2.h b/include/linux/jbd2.h
> index 9986ab8..8d95314 100644
> --- a/include/linux/jbd2.h
> +++ b/include/linux/jbd2.h
> @@ -56,17 +56,13 @@
> */
> #define JBD2_EXPENSIVE_CHECKING
> extern ushort jbd2_journal_enable_debug;
> +void __jbd2_debug(int level, const char *file, const char *func,
> + unsigned int line, const char *fmt, ...);
>
> -#define jbd_debug(n, f, a...) \
> - do { \
> - if ((n) <= jbd2_journal_enable_debug) { \
> - printk (KERN_DEBUG "(%s, %d): %s: ", \
> - __FILE__, __LINE__, __func__); \
> - printk (f, ## a); \
> - } \
> - } while (0)
> +#define jbd_debug(n, fmt, a...) \
> + __jbd2_debug((n), __FILE__, __func__, __LINE__, (fmt), ##a)
> #else
> -#define jbd_debug(f, a...) /**/
> +#define jbd_debug(n, fmt, a...) /**/
> #endif
>
> extern void *jbd2_alloc(size_t size, gfp_t flags);
>
--
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