From: Dave Jones <davej@redhat.com>
To: Hugh Dickins <hughd@google.com>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: shmem_getpage_gfp VM_BUG_ON triggered. [3.7rc2]
Date: Thu, 1 Nov 2012 21:43:36 -0400 [thread overview]
Message-ID: <20121102014336.GA1727@redhat.com> (raw)
In-Reply-To: <alpine.LNX.2.00.1211011627120.19567@eggly.anvils>
On Thu, Nov 01, 2012 at 04:48:41PM -0700, Hugh Dickins wrote:
> On Thu, 1 Nov 2012, Dave Jones wrote:
> > On Thu, Nov 01, 2012 at 04:03:40PM -0700, Hugh Dickins wrote:
> > >
> > > Except... earlier in the thread you explained how you hacked
> > > #define VM_BUG_ON(cond) WARN_ON(cond)
> > > to get this to come out as a warning instead of a bug,
> > > and now it looks as if "a user" has here done the same.
> > >
> > > Which is very much a user's right, of course; but does
> > > make me wonder whether that user might actually be davej ;)
> >
> > indirectly. I made the same change in the Fedora kernel a while ago
> > to test a hypothesis that we weren't getting any VM_BUG_ON reports.
>
> Fedora turns on CONFIG_DEBUG_VM?
Yes.
> All mm developers should thank you for the wider testing exposure;
> but I'm not so sure that Fedora users should thank you for turning
> it on - really it's for mm developers to wrap around !assertions or
> more expensive checks (e.g. checking calls) in their development.
The last time I did some benchmarking the impact wasn't as ridiculous
as say lockdep, or spinlock debug. Maybe the benchmarks I was using
weren't pushing the VM very hard, but it seemed to me that the value
in getting info in potential problems early was higher than a small
performance increase.
> Or did I read a few months ago that some change had been made to
> such definitions, and VM_BUG_ON(contents) are evaluated even when
> the config option is off? I do hope I'm mistaken on that.
Pretty sure that isn't the case. I remember Andrew chastising people
a few times for putting checks in VM_BUG_ON's that needed to stay around
even when the config option was off. Perhaps you were thinking of one
of those incidents ?
Dave
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WARNING: multiple messages have this Message-ID (diff)
From: Dave Jones <davej@redhat.com>
To: Hugh Dickins <hughd@google.com>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: shmem_getpage_gfp VM_BUG_ON triggered. [3.7rc2]
Date: Thu, 1 Nov 2012 21:43:36 -0400 [thread overview]
Message-ID: <20121102014336.GA1727@redhat.com> (raw)
In-Reply-To: <alpine.LNX.2.00.1211011627120.19567@eggly.anvils>
On Thu, Nov 01, 2012 at 04:48:41PM -0700, Hugh Dickins wrote:
> On Thu, 1 Nov 2012, Dave Jones wrote:
> > On Thu, Nov 01, 2012 at 04:03:40PM -0700, Hugh Dickins wrote:
> > >
> > > Except... earlier in the thread you explained how you hacked
> > > #define VM_BUG_ON(cond) WARN_ON(cond)
> > > to get this to come out as a warning instead of a bug,
> > > and now it looks as if "a user" has here done the same.
> > >
> > > Which is very much a user's right, of course; but does
> > > make me wonder whether that user might actually be davej ;)
> >
> > indirectly. I made the same change in the Fedora kernel a while ago
> > to test a hypothesis that we weren't getting any VM_BUG_ON reports.
>
> Fedora turns on CONFIG_DEBUG_VM?
Yes.
> All mm developers should thank you for the wider testing exposure;
> but I'm not so sure that Fedora users should thank you for turning
> it on - really it's for mm developers to wrap around !assertions or
> more expensive checks (e.g. checking calls) in their development.
The last time I did some benchmarking the impact wasn't as ridiculous
as say lockdep, or spinlock debug. Maybe the benchmarks I was using
weren't pushing the VM very hard, but it seemed to me that the value
in getting info in potential problems early was higher than a small
performance increase.
> Or did I read a few months ago that some change had been made to
> such definitions, and VM_BUG_ON(contents) are evaluated even when
> the config option is off? I do hope I'm mistaken on that.
Pretty sure that isn't the case. I remember Andrew chastising people
a few times for putting checks in VM_BUG_ON's that needed to stay around
even when the config option was off. Perhaps you were thinking of one
of those incidents ?
Dave
next prev parent reply other threads:[~2012-11-02 1:43 UTC|newest]
Thread overview: 69+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-10-25 2:37 shmem_getpage_gfp VM_BUG_ON triggered. [3.7rc2] Dave Jones
2012-10-25 2:37 ` Dave Jones
2012-10-25 4:36 ` Hugh Dickins
2012-10-25 4:36 ` Hugh Dickins
2012-10-25 4:50 ` Ni zhan Chen
2012-10-25 4:50 ` Ni zhan Chen
2012-10-25 6:59 ` Hugh Dickins
2012-10-25 6:59 ` Hugh Dickins
2012-10-25 9:53 ` Ni zhan Chen
2012-10-25 10:21 ` Ni zhan Chen
2012-10-25 10:21 ` Ni zhan Chen
2012-10-25 21:27 ` Hugh Dickins
2012-10-25 21:27 ` Hugh Dickins
2012-10-26 1:48 ` Ni zhan Chen
2012-10-26 1:48 ` Ni zhan Chen
2012-10-25 11:14 ` Dave Jones
2012-10-25 11:14 ` Dave Jones
2012-10-25 21:28 ` Hugh Dickins
2012-10-25 21:28 ` Hugh Dickins
2012-10-25 20:52 ` Johannes Weiner
2012-10-25 20:52 ` Johannes Weiner
2012-10-25 21:48 ` Hugh Dickins
2012-10-25 21:48 ` Hugh Dickins
2012-10-26 2:15 ` Ni zhan Chen
2012-10-26 2:15 ` Ni zhan Chen
2012-11-01 19:10 ` Dave Jones
2012-11-01 19:10 ` Dave Jones
2012-11-01 23:03 ` Hugh Dickins
2012-11-01 23:03 ` Hugh Dickins
2012-11-01 23:20 ` Dave Jones
2012-11-01 23:20 ` Dave Jones
2012-11-01 23:48 ` Hugh Dickins
2012-11-01 23:48 ` Hugh Dickins
2012-11-02 1:43 ` Dave Jones [this message]
2012-11-02 1:43 ` Dave Jones
2012-11-02 23:26 ` Hugh Dickins
2012-11-02 23:26 ` Hugh Dickins
2012-11-06 1:32 ` [PATCH] tmpfs: fix shmem_getpage_gfp VM_BUG_ON Hugh Dickins
2012-11-06 1:32 ` Hugh Dickins
2012-11-06 13:54 ` Dave Jones
2012-11-06 13:54 ` Dave Jones
2012-11-06 23:48 ` Hugh Dickins
2012-11-06 23:48 ` Hugh Dickins
2012-11-07 22:38 ` Dave Jones
2012-11-07 22:38 ` Dave Jones
2012-11-14 1:36 ` [PATCH] tmpfs: fix shmem_getpage_gfp VM_BUG_ON fix Hugh Dickins
2012-11-14 1:36 ` Hugh Dickins
2012-11-14 3:07 ` [PATCH] tmpfs: fix shmem_getpage_gfp VM_BUG_ON Jaegeuk Hanse
2012-11-14 3:07 ` Jaegeuk Hanse
2012-11-14 3:50 ` Hugh Dickins
2012-11-14 3:50 ` Hugh Dickins
2012-11-14 6:14 ` Dave Jones
2012-11-14 6:14 ` Dave Jones
2012-11-14 10:06 ` Hugh Dickins
2012-11-14 10:06 ` Hugh Dickins
2012-11-15 7:39 ` Jaegeuk Hanse
2012-11-15 7:39 ` Jaegeuk Hanse
2012-11-15 19:56 ` Hugh Dickins
2012-11-15 19:56 ` Hugh Dickins
2012-11-16 0:40 ` Jaegeuk Hanse
2012-11-16 0:40 ` Jaegeuk Hanse
2012-11-16 9:34 ` Jaegeuk Hanse
2012-11-16 9:34 ` Jaegeuk Hanse
2012-11-17 4:48 ` Hugh Dickins
2012-11-17 4:48 ` Hugh Dickins
2012-11-18 0:57 ` Jaegeuk Hanse
2012-11-18 0:57 ` Jaegeuk Hanse
2012-11-18 1:48 ` Jaegeuk Hanse
2012-11-18 1:48 ` Jaegeuk Hanse
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