Re: [PATCH v3] iomap: add allocation cache for iomap_dio

["changfengnan" <changfengnan@bytedance.com>]

> From: "Christoph Hellwig"<hch@infradead.org>
> Date:  Tue, Mar 17, 2026, 17:13
> Subject:  Re: [PATCH v3] iomap: add allocation cache for iomap_dio
> To: "changfengnan"<changfengnan@bytedance.com>
> Cc: "Vlastimil Babka (SUSE)"<vbabka@kernel.org>, "Dave Chinner"<david@fromorbit.com>, "Harry Yoo"<harry.yoo@oracle.com>, "Hao Li"<hao.li@linux.dev>, "guzebing"<guzebing1612@gmail.com>, <brauner@kernel.org>, <djwong@kernel.org>, <hch@infradead.org>, <linux-xfs@vger.kernel.org>, <linux-fsdevel@vger.kernel.org>, <linux-kernel@vger.kernel.org>, <guzebing@bytedance.com>, <syzbot@syzkaller.appspotmail.com>, <linux-mm@kvack.org>
> On Tue, Mar 17, 2026 at 04:33:24PM +0800, changfengnan wrote:
> > > IO is not my area but getting from 1.19M to 1.20M doesn't look like it's
> > > worth the custom code? (possibly from 1.17M to 1.20M it also wasn't).
> > Yes, at least for now, there’s no need for a per-CPU.
> > It might be better to replace kmalloc with a new cache, but my tests so far
> > haven’t shown any performance improvements.  I’ll look into it further.
> 
> Does using a kmem_cache help?  That should generally be a nice win
> anyway due to keeping the objects together.
For now, my test case is just run ./t/io_uring and fio, no other process, not show
any performance improvements, test case is simple and no other user try to
kmalloc same size object, I think maybe there will be improvements in more
complex case. In theory, yes. I’ll run some tests to verify that.
>