Re: [rfc][patch] remove racy sync_page?

Nick Piggin wrote:

Linus Torvalds wrote:

Tell me WHERE you can unplug in that sequence. I will tell you where you can NOT unplug:

...

- you can NOT just unplug in the path _after_ "readpage()", because the IO may have been started by SOMEBODY ELSE that just did read-ahead, and didn't unplug (on _purpose_ - the whole point of doing read-ahead is to allow concurrent IO execution, so a read-aheader that unplugs is broken by definition)

Umm, this happens with the current lock_page() after readpage. And
with per-task plugs, you do not unplug anybody else.

If this wasn't clear: I don't mean per-task plugs as in "the task
explicitly plugs and unplugs the block device"[*]; I mean really
per-task plugs.

[*] That would be crazy anyway because that would imply some random
    task can plug an filled request queue that is going full tilt.

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