On Wed, 9 Sep 2020, Matthew Wilcox wrote: > On Wed, Sep 09, 2020 at 11:24:14AM -0700, Hugh Dickins wrote: > > After overnight reflection, my own preference would be simply to > > drop this patch. I think we are making altogether too much of a > > fuss here over what was simply correct as plain put_page() > > (and further from correct if we change it to leak the page in an > > unforeseen circumstance). > > > > And if Alex's comment was not quite grammatically correct, never mind, > > it said as much as was worth saying. I got more worried by his > > placement of the "busy:" label, but that does appear to work correctly. > > > > There's probably a thousand places where put_page() is used, where > > it would be troublesome if it were the final put_page(): this one > > bothered you because you'd been looking at isolate_migratepages_block(), > > and its necessary avoidance of lru_lock recursion on put_page(); > > but let's just just leave this put_page() as is. > > My problem with put_page() is that it's no longer the simple > decrement-and-branch-to-slow-path-if-zero that it used to be. It has the > awful devmap excrement in it so it really expands into a lot of code. > I really wish that "feature" could be backed out again. It clearly > wasn't ready for merge. And I suppose I should thank you for opening my eyes to that. I knew there was "dev" stuff inside __put_page(), but didn't realize that the inline put_page() has now been defiled. Yes, I agree, that is horrid and begs to be undone. But this is not the mail thread for discussing that, and we should not use strange alternatives to put_page(), here or elsewhere, just to avoid that (surely? hopefully?) temporary excrescence. Hugh
