Because usually that's what we want. See, for example, fs/mpage.c:

while ((page = readahead_page(rac))) { prefetchw(&page->flags); args.page = page; args.nr_pages = readahead_count(rac); args.bio = do_mpage_readpage(&args); put_page(page); }

fuse is different because it's trying to allocate for the next batch, not for the batch we're currently on.

I'm a little annoyed because I posted almost this exact loop here:

https://lore.kernel.org/linux-fsdevel/CAJfpegtrhGamoSqD-3Svfj3-iTdAbfD8TP44H_o+HE+g+CAnCA@xxxxxxxxxxxxxx/

and you said "I think that's fine", modified only by your concern for it not being obvious that nr_pages couldn't be decremented by __readahead_batch(), so I modified the loop slightly to assign to nr_pages. The part you're now complaining about is unchanged.

> > + if (nr_pages > max_pages) > > + nr_pages = max_pages; > > + if (nr_pages == 0) > > + break; > > + ia = fuse_io_alloc(NULL, nr_pages); > > + if (!ia) > > + return; > > + ap = &ia->ap; > > + nr_pages = __readahead_batch(rac, ap->pages, nr_pages); > > + for (i = 0; i < nr_pages; i++) { > > + fuse_wait_on_page_writeback(inode, > > + readahead_index(rac) + i); > > What's wrong with ap->pages[i]->index? Are we trying to wean off using ->index?

It saves reading from a cacheline? I wouldn't be surprised if the compiler hoisted the read from rac->_index to outside the loop and just iterated from rac->_index to rac->_index + nr_pages.