Re: [PATCHv2 1/1] ext4: mballoc: Use this_cpu_read instead of this_cpu_ptr

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 





On 6/9/20 6:07 PM, Hillf Danton wrote:

On Tue, 9 Jun 2020 18:53:23 +0800 Ritesh Harjani wrote:

Simplify reading a seq variable by directly using this_cpu_read API
instead of doing this_cpu_ptr and then dereferencing it.

Two of the quick questions
1) Why can blocks discarded in a ext4 FS help allocators in another?

I am not sure if I understand your Q correctly. But here is a brief about the patchset. If there were PA blocks just or about to be discarded by another thread, then the current thread who is doing block allocation should not fail with ENOSPC error instead should be able to allocate those blocks from another thread. The concept is better explained in the commit msgs, if more details are required. Without this patchset (in some heavy multi-threaded use case) allocation was failing when the overall filesystem space available was more then 50%.


2) Why is a percpu seqcount prefered over what <linux/seqlock.h>
can offer?


Since this could be a multi-threaded use case, per cpu variable helps in avoid cache line bouncing problem, which could happen when the same variable is updated by multiple threads on different cpus.

-ritesh



[Index of Archives]     [Reiser Filesystem Development]     [Ceph FS]     [Kernel Newbies]     [Security]     [Netfilter]     [Bugtraq]     [Linux FS]     [Yosemite National Park]     [MIPS Linux]     [ARM Linux]     [Linux Security]     [Linux RAID]     [Samba]     [Device Mapper]     [Linux Media]

  Powered by Linux