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Date: Wed, 19 Feb 2020 09:48:29 +1100 From: Dave Chinner <david@...morbit.com> To: Matthew Wilcox <willy@...radead.org> Cc: linux-fsdevel@...r.kernel.org, linux-mm@...ck.org, linux-kernel@...r.kernel.org, linux-btrfs@...r.kernel.org, linux-erofs@...ts.ozlabs.org, linux-ext4@...r.kernel.org, linux-f2fs-devel@...ts.sourceforge.net, cluster-devel@...hat.com, ocfs2-devel@....oracle.com, linux-xfs@...r.kernel.org Subject: Re: [PATCH v6 04/19] mm: Rearrange readahead loop On Tue, Feb 18, 2020 at 05:57:36AM -0800, Matthew Wilcox wrote: > On Tue, Feb 18, 2020 at 04:08:24PM +1100, Dave Chinner wrote: > > On Mon, Feb 17, 2020 at 10:45:45AM -0800, Matthew Wilcox wrote: > > > From: "Matthew Wilcox (Oracle)" <willy@...radead.org> > > > > > > Move the declaration of 'page' to inside the loop and move the 'kick > > > off a fresh batch' code to the end of the function for easier use in > > > subsequent patches. > > > > Stale? the "kick off" code is moved to the tail of the loop, not the > > end of the function. > > Braino; I meant to write end of the loop. > > > > @@ -183,14 +183,14 @@ void __do_page_cache_readahead(struct address_space *mapping, > > > page = xa_load(&mapping->i_pages, page_offset); > > > if (page && !xa_is_value(page)) { > > > /* > > > - * Page already present? Kick off the current batch of > > > - * contiguous pages before continuing with the next > > > - * batch. > > > + * Page already present? Kick off the current batch > > > + * of contiguous pages before continuing with the > > > + * next batch. This page may be the one we would > > > + * have intended to mark as Readahead, but we don't > > > + * have a stable reference to this page, and it's > > > + * not worth getting one just for that. > > > */ > > > - if (readahead_count(&rac)) > > > - read_pages(&rac, &page_pool, gfp_mask); > > > - rac._nr_pages = 0; > > > - continue; > > > + goto read; > > > } > > > > > > page = __page_cache_alloc(gfp_mask); > > > @@ -201,6 +201,11 @@ void __do_page_cache_readahead(struct address_space *mapping, > > > if (page_idx == nr_to_read - lookahead_size) > > > SetPageReadahead(page); > > > rac._nr_pages++; > > > + continue; > > > +read: > > > + if (readahead_count(&rac)) > > > + read_pages(&rac, &page_pool, gfp_mask); > > > + rac._nr_pages = 0; > > > } > > > > Also, why? This adds a goto from branched code that continues, then > > adds a continue so the unbranched code doesn't execute the code the > > goto jumps to. In absence of any explanation, this isn't an > > improvement and doesn't make any sense... > > I thought I was explaining it ... "for easier use in subsequent patches". Sorry, my braino there. :) I commented on the problem with the first part of the sentence, then the rest of the sentence completely failed to sink in. -Dave. -- Dave Chinner david@...morbit.com
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