Re: [PATCH v5 07/14] iomap: track pending read bytes more optimally

["Darrick J. Wong" <djwong@kernel.org>]

On Fri, Oct 24, 2025 at 09:59:01PM +0100, Matthew Wilcox wrote:
> On Fri, Oct 24, 2025 at 12:22:32PM -0700, Joanne Koong wrote:
> > > Feels like more filesystem people should be enabling CONFIG_DEBUG_VM
> > > when testing (excluding performance testing of course; it'll do ugly
> > > things to your performance numbers).
> > 
> > Point taken. It looks like there's a bunch of other memory debugging
> > configs as well. Do you recommend enabling all of these when testing?
> > Do you have a particular .config you use for when you run tests?
> 
> Our Kconfig is far too ornate.  We could do with a "recommended for
> kernel developers" profile.  Here's what I'm currently using, though I
> know it's changed over time:

Is there any chance you could split the VM debug checks into cheap and
expensive ones, and create another kconfig option so that we could do
the cheap checks without having fstests take a lot longer?

You could also implement shenanigans like the following:
https://git.kernel.org/pub/scm/linux/kernel/git/djwong/xfs-linux.git/commit/?h=djwong-wtf&id=b739fff870384fd239abfd99ecee6bc47640794d

To enable the expensive checks at runtime.

(Yeah, I know, this is probably a 2 year project + bikeshed score of at
least 30...)

--D

> CONFIG_X86_DEBUGCTLMSR=y
> CONFIG_PM_DEBUG=y
> CONFIG_PM_SLEEP_DEBUG=y
> CONFIG_ARCH_SUPPORTS_DEBUG_PAGEALLOC=y
> CONFIG_BLK_DEBUG_FS=y
> CONFIG_PNP_DEBUG_MESSAGES=y
> CONFIG_SCSI_DEBUG=m
> CONFIG_EXT4_DEBUG=y
> CONFIG_JFS_DEBUG=y
> CONFIG_XFS_DEBUG=y
> CONFIG_BTRFS_DEBUG=y
> CONFIG_UFS_DEBUG=y
> CONFIG_DEBUG_BUGVERBOSE=y
> CONFIG_DEBUG_KERNEL=y
> CONFIG_DEBUG_MISC=y
> CONFIG_DEBUG_INFO=y
> CONFIG_DEBUG_INFO_DWARF4=y
> CONFIG_DEBUG_INFO_COMPRESSED_NONE=y
> CONFIG_DEBUG_FS=y
> CONFIG_DEBUG_FS_ALLOW_ALL=y
> CONFIG_ARCH_HAS_EARLY_DEBUG=y
> CONFIG_SLUB_DEBUG=y
> CONFIG_ARCH_HAS_DEBUG_WX=y
> CONFIG_HAVE_DEBUG_KMEMLEAK=y
> CONFIG_SHRINKER_DEBUG=y
> CONFIG_ARCH_HAS_DEBUG_VM_PGTABLE=y
> CONFIG_DEBUG_VM_IRQSOFF=y
> CONFIG_DEBUG_VM=y
> CONFIG_ARCH_HAS_DEBUG_VIRTUAL=y
> CONFIG_DEBUG_MEMORY_INIT=y
> CONFIG_LOCK_DEBUGGING_SUPPORT=y
> CONFIG_DEBUG_RT_MUTEXES=y
> CONFIG_DEBUG_SPINLOCK=y
> CONFIG_DEBUG_MUTEXES=y
> CONFIG_DEBUG_WW_MUTEX_SLOWPATH=y
> CONFIG_DEBUG_RWSEMS=y
> CONFIG_DEBUG_LOCK_ALLOC=y
> CONFIG_DEBUG_LIST=y
> CONFIG_X86_DEBUG_FPU=y
> CONFIG_FAULT_INJECTION_DEBUG_FS=y
> 
> (output from grep DEBUG .build/.config |grep -v ^#)