Re: [GIT PULL] iov_iter: Improve page extraction (pin or just list)

Jens Axboe
2023-01-30T21:56:05Z

On 1/30/23 2:33 PM, Jens Axboe wrote:
> On 1/30/23 4:14 AM, David Howells wrote:
>> Hi Jens,
>>
>> Could you consider pulling this patchset into the block tree? I think that
>> Al's fears wrt to pinned pages being removed from page tables causing deadlock
>> have been answered. Granted, there is still the issue of how to handle
>> vmsplice and a bunch of other places to fix, not least skbuff handling.
>>
>> I also have patches to fix cifs in a separate branch that I would also like to
>> push in this merge window - and that requires the first two patches from this
>> series also, so would it be possible for you to merge at least those two
>> rather than manually applying them?
>
> I've pulled this into a separate branch, but based on the block branch,
> for-6.3/iov-extract. It's added to for-next as well.

This does cause about a 2.7% regression for me, using O_DIRECT on a raw
block device. Looking at a perf diff, here's the top:

+2.71% [kernel.vmlinux] [k] mod_node_page_state
+2.22% [kernel.vmlinux] [k] iov_iter_extract_pages

and these two are gone:

2.14% [kernel.vmlinux] [k] __iov_iter_get_pages_alloc
1.53% [kernel.vmlinux] [k] iov_iter_get_pages

rest is mostly in the noise, but mod_node_page_state() sticks out like
a sore thumb. They seem to be caused by the node stat accounting done
in gup.c for FOLL_PIN.

Hmm?

--
Jens Axboe