| Message ID | 20180518164830.1552-9-hch@lst.de (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
On Fri, May 18, 2018 at 06:48:04PM +0200, Christoph Hellwig wrote: > That way file systems don't have to go spotting for non-contiguous pages > and work around them. It also kicks off I/O earlier, allowing it to > finish earlier and reduce latency. > > Signed-off-by: Christoph Hellwig <hch@lst.de> > --- > mm/readahead.c | 12 +++++++++++- > 1 file changed, 11 insertions(+), 1 deletion(-) > > diff --git a/mm/readahead.c b/mm/readahead.c > index fa4d4b767130..044ab0c137cc 100644 > --- a/mm/readahead.c > +++ b/mm/readahead.c > @@ -177,8 +177,18 @@ unsigned int __do_page_cache_readahead(struct address_space *mapping, > rcu_read_lock(); > page = radix_tree_lookup(&mapping->i_pages, page_offset); > rcu_read_unlock(); > - if (page && !radix_tree_exceptional_entry(page)) > + if (page && !radix_tree_exceptional_entry(page)) { > + /* > + * Page already present? Kick off the current batch of > + * contiguous pages before continuing with the next > + * batch. > + */ > + if (nr_pages) > + read_pages(mapping, filp, &page_pool, nr_pages, > + gfp_mask); > + nr_pages = 0; > continue; > + } The comment at the top of this function explicitly states that we don't submit I/Os before all of the pages are allocated. That probably needs an update, at least. That aside, couldn't this introduce that kind of problematic read/write behavior if the mapping was sparsely populated for whatever reason (every other page, for example)? Perhaps that's just too unlikely to matter. Brian > > page = __page_cache_alloc(gfp_mask); > if (!page) > -- > 2.17.0 > > -- > To unsubscribe from this list: send the line "unsubscribe linux-xfs" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe linux-xfs" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/mm/readahead.c b/mm/readahead.c index fa4d4b767130..044ab0c137cc 100644 --- a/mm/readahead.c +++ b/mm/readahead.c @@ -177,8 +177,18 @@ unsigned int __do_page_cache_readahead(struct address_space *mapping, rcu_read_lock(); page = radix_tree_lookup(&mapping->i_pages, page_offset); rcu_read_unlock(); - if (page && !radix_tree_exceptional_entry(page)) + if (page && !radix_tree_exceptional_entry(page)) { + /* + * Page already present? Kick off the current batch of + * contiguous pages before continuing with the next + * batch. + */ + if (nr_pages) + read_pages(mapping, filp, &page_pool, nr_pages, + gfp_mask); + nr_pages = 0; continue; + } page = __page_cache_alloc(gfp_mask); if (!page)
That way file systems don't have to go spotting for non-contiguous pages and work around them. It also kicks off I/O earlier, allowing it to finish earlier and reduce latency. Signed-off-by: Christoph Hellwig <hch@lst.de> --- mm/readahead.c | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-)