On Wed, Sep 15, 2021 at 01:21:30PM +1000, Alistair Popple wrote: > On Wednesday, 15 September 2021 12:52:48 PM AEST Peter Xu wrote: > > > > > The flag introduced in this patch will be a preparation for more bits defined > > > > in the future, e.g., for a new bit in flag to show whether to persist the > > > > upcoming uffd-wp bit in pgtable entries. > > > > > > That's kind of the problem. The patch itself looks correct to me however as > > > mentioned it is mostly reverting a previous cleanup and it's hard to tell why > > > that's justified without the subsequent patches. Perhaps it makes the usage of > > > zap_details a bit clearer, but a comment also would with less code. > > > > > > I know you want to try and shrink the uffd-wp series but I think this patch > > > might be easier to review if it was included as part of that series. > > > > I posted it because I think it's suitable to have it even without uffd-wp. > > > > I tried to explain it above on two things this patch wanted to fix: > > > > Firstly the comment is wrong; we've moved back and forth on changing the > > zap_details flags but the comment is not changing along the way and it's not > > matching the code right now. > > > > Secondly I do think we should have a flag showing explicit willingness to skip > > swap entries. Yes, uffd-wp is the planned new one, but my point is anyone who > > will introduce a new user of zap_details pointer could overlook this fact. The > > new flag helps us to make sure someone will at least read the flags and know > > what'll happen with it. > > > > For the 2nd reasoning, I also explicitly CCed Kirill too, so Kirill can provide > > any comment if he disagrees. For now, I still think we should keep having such > > a flag otherwise it could be error-prone. > > > > Could you buy-in above reasoning? > > Kind of, I do think it makes the usage of details a bit clearer or at least > harder to miss. It is just that if that was the sole aim of this patch I think > there might be simpler (less code) ways of doing so. Yes you're right, we can add a big enough comment above zap_details to state that, but then it'll be reverted when adding the uffd-wp flag in the other series, because uffd-wp will still needs a way to specify !SKIP_SWAP and KEEP_UFFD_WP. Then it'll make the "series split" make less sense as you said. I split the series only because I hope it could ease the reviewers, and also that's probably the only thing I can do now to still try to smooth the process of having a complete uffd-wp finally got proper reviewed and merged. > > > Basically above is what I wanted to express in my commit message. I hope that > > can justify that this patch (even if extremly simple) can still be considered > > as acceptable upstream even without uffd-wp series. > > > > If you still insist on this patch not suitable for standalone merging and > > especially if some other reviewer would think the same, I can move it back to > > uffd-wp series for sure. Then I'll repost this series with 4 patches only. > > I won't insist, the code looks correct and it doesn't make things any less > clear so you can put my Reviewed-by on it and perhaps leave it to Andrew or > another reviewer to determine if this should be taken in this series or as part > of a future uffd-wp series. Will do; thanks. -- Peter Xu
