On Sun, May 17, 2020 at 09:21:05PM +0100, David Howells wrote: > Don't call req->page_done() on each page as we finish filling it with the > data coming from the network. Whilst this might speed up the application a > bit, it's a problem if there's a network failure and the operation has to > be reissued. It's readpages, which by definition is called for pages that the application is _not_ currently waiting for. Now, if the application is multithreaded and happens to want pages that are currently under ->readpages, then that's going to be a problem (but also unlikely). Also if the application overruns the readahead window then it'll have to wait a little longer (but we ramp up the readahead window, so this should be a self-correcting problem). > If this happens, an oops occurs because afs_readpages_page_done() clears > the pointer to each page it unlocks and when a retry happens, the pointers > to the pages it wants to fill are now NULL (and the pages have been > unlocked anyway). I mean, you could check for NULL pointers and not issue the I/O for that region ... but it doesn't seem necessary. > Instead, wait till the operation completes successfully and only then > release all the pages after clearing any terminal gap (the server can give > us less data than we requested as we're allowed to ask for more than is > available). s/release/mark up to date/ > + if (req->page_done) > + for (req->index = 0; req->index < req->nr_pages; req->index++) > + req->page_done(req); > + I'd suggest doing one call rather than N and putting the page iteration inside the callback. But this patch is appropriate for this late in the -rc series, just something to consider for the future. You might even want to use a bit in the req to indicate whether this is a readahead request ... that's the only user of the ->page_done callback that I can find. Anyway, Reviewed-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
