Andrew Morton replied to a commit message making 4k stacks the default, saying, "this patch will cause kernels to crash." Ingo Molnar replied, "what mainline kernels crash and how will they crash? Fedora and other distros have had 4K stacks enabled for years." He added, "we've conducted tens of thousands of bootup tests with all sorts of drivers and kernel options enabled and have yet to see a single crash due to 4K stacks." During the lengthy discussion it was suggested that nfs+xfs+raid kernel configurations, and using ndiswrapper are the most common reasons for overflowing a 4K stack size.

Andi Kleen questioned the usefulness of 4k stacks, "as far as I can figure out they are not [a worthy goal]. They might have been a worthy goal on crappy 2.4 VMs, but these times are long gone." Arjan van de Ven suggested that though the 2.6 VM is much improved over the 2.4 VM, fragmentation with 8K stacks remains an unsolvable problem, "it's basic math; the Linux VM gets to deal with both short and long lasting allocations; no matter how hard you try to get some degree of fragmentation; especially due to the 15:1 acceleration you get due to the lowmem issue. And before you say 'you should use 64 bit on such machines'; I would love it if more people used 64 bit linux. Sadly the adoption rate of that is not very good still.... by far ;(" In another email, Arjan listed two advantages to 4K stacks, "1) less memory consumption in the lowmem zone (critical for enterprise use, also good for general performance), and 2) kernel stacks at 8K are one of the most prominent order-1 allocations in the kernel; again with big-memory systems the fragmentation of the lowmem zone is a problem (and the distros that ship 4K stacks went there because of customer complaints)".

In a series of 5 patches, Jesper Juhl propsed moving 4K stacks from a debug feature to a non-debug feature, defaulting it to be enabled in the -mm tree. He referred back to a lengthy earlier discussion in which he had proposed making 4K stacks the default in the mainline kernel, then added:

"Based on the comments in that thread I conclude that 4KSTACKS are not really considered a debug-only feature any longer, but the time is not right (yet) to make them the default - and it's certainly not yet the time to get rid of 8K stacks."

"In that thread I promised to provide some patches that would lift 4KSTACKS out of debug-only feature status, which is what the first two patches in this series do. I also said I would provide a patch to make 4KSTACKS 'default y' to get more testing, but restrict that patch to -mm - that's the fifth patch in this series. Patches 3 & 4 in this series move the config option out of the Kernel hacking menu and into Processor types and features".

Hans Reiser [interview] described a recently posted patch as, "it revises the existing reiser4 code to do a good job for writes that are larger than 4k at a time by assiduously adhering to the principle that things that need to be done once per write should be done once per write, not once per 4k." He went on to explain, "this code empirically proves that the generic code design which passes 4k at a time to the underlying FS can be improved. Performance results show that the new code consumes 40% less CPU when doing 'dd bs=1MB .....'" Referring to generic_file_write(), he further noted that currently when writing 64MB of data, "it may go to the kernel as a 64MB write, but VFS sends it to the FS as 64MB/4k separate 4k writes." It was acknowledged that this could also be accomplished in a non-generic way, howevever earlier feedback had suggested that such improvements should be made available to all.

Andrew Morton [interview] responded to the proposed changes saying, "there's nothing which leaps out and says 'wrong' in this. But there's nothing which leaps out and says 'right', either. It seems somewhat arbitrary, that's all." He pointed out that reiser4 was currently the only filesystem to benefit from the changes, "to be able to say 'yes, we want this' I think we'd need to understand which other filesystems would benefit from exploiting it, and with what results?" In the resulting discussion, it was determined that both FUSE [story] and XFS [story] would benefit from these changes prompting Hans to ask, "Is it enough?" Andrew agreed, "Spose so. Let's see what the diff looks like?"

Hans Reiser [interview] sent an email to the lkml titled, "I request inclusion of reiser4 in the mainline kernel". He provided a list of objections raised earlier, noting that all had been addressed. Among the listed issues, Reiser4 now works with 4k stacks. "There have been no bug reports concerning the new code," Hans added.

The request was followed with some suggestions by Christoph Hellwig, including general comments about the coding style. This was one of many issues that led to debate in which Hans commented, "most of my customers remark that Namesys code is head and shoulders above the rest of the kernel code. So yes, it is different." Alan Cox [interview] replied that while the kernel coding style isn't his own style, he tries to follow it when working on the kernel, "one big reason we jump up and down so much about the coding style is that its the one thing that ensures someone else can maintain and fix code that the author has abandoned, doesn't have time to fix or that needs access to specific hardware the authors may not have." Much of the rest of the thread was less friendly, leaving the question of merging Reiser4 into the mainline kernel still up in the air.