Re: [PATCH] mm,shmem: Fix a typo in shmem_swapin_page()

On Mon, Aug 9, 2021 at 4:43 PM Huang, Ying [off-list ref] wrote:

Yang Shi [off-list ref] writes:

quoted

On Fri, Aug 6, 2021 at 1:37 PM Yang Shi [off-list ref] wrote:

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On Thu, Aug 5, 2021 at 11:01 PM Hugh Dickins [off-list ref] wrote:

quoted

On Thu, 5 Aug 2021, Yang Shi wrote:

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On Tue, Aug 3, 2021 at 10:34 PM Hugh Dickins [off-list ref] wrote:

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I've never seen the swapoff race claimed by Miaohe, and don't expect to;
but he's probably right, given the current code.  I just dislike adding
unnecessary complexity, and siting it in the wrong place (mm/shmem.c).

Yang, is it possible that 5.1 commit 8fd2e0b505d1 ("mm: swap: check if
swap backing device is congested or not") was actually developed and
measured on 4.1 or earlier, which still had blk_set_queue_congested()?

I forgot the exact version, but definitely not 4.1 or earlier. Maybe
4.19 or earlier. I'm not familiar with how block layer detect
congestion, if the logic was changed, hence the optimization doesn't
stand anymore nowadays, I'm totally fine to remove it.

You drove me back to look more closely.  blk_set_queue_congested()
vanished from include/linux/blkdev.h in 4.2, but blk_set_congested()
appeared then in block/blk-core.c to replace it.  blk_set_congested()
vanished (along with all references to "congested" in blk-core.c) in
5.0, then your commit (most probably tested on 4.19) went into 5.1 -
just after it had become redundant!

Thanks, yes, let's revert that and Miaohe's and Huang's, later on.

It should be easier to revert Huang Ying's , then Miaohe's, then mine.

Hi Ying,

I just prepared the reverts since I need to revert yours and Miaohe's
in order to revert my problematic commit.

If your original commit will be reverted, then mine and Miaohe's can be
reverted from the race condition point of view.

Yes, this is exactly what I did.

Although I still think it's better to call get/put_swap_device() in
shmem_swapin_page(), that can be discussed with another patch.

Any additional change could be based off the reverts.

Best Regards,
Huang, Ying