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charset="UTF-8" X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tue, Sep 22, 2020 at 10:02 AM Rik van Riel wrote: > > Check whether a swap page was obtained instantaneously, for example > because it is in zswap, or on a very fast IO device which uses busy > waiting, and we did not wait on IO to swap in this page. > If no IO was needed to get the swap page we want, kicking off readahead > on surrounding swap pages is likely to be counterproductive, because the > extra loads will cause additional latency, use up extra memory, and chances > are the surrounding pages in swap are just as fast to load as this one, > making readahead pointless. > > Signed-off-by: Rik van Riel > --- > mm/swap_state.c | 14 +++++++++++--- > 1 file changed, 11 insertions(+), 3 deletions(-) > > diff --git a/mm/swap_state.c b/mm/swap_state.c > index aacb9ba53f63..6919f9d5fe88 100644 > --- a/mm/swap_state.c > +++ b/mm/swap_state.c > @@ -637,6 +637,7 @@ static struct page *swap_cluster_read_one(swp_entry_t entry, > struct page *swap_cluster_readahead(swp_entry_t entry, gfp_t gfp_mask, > struct vm_fault *vmf) Why not do this for swap_vma_readahead() too? swap_cluster_read_one() can be used in swap_vma_readahead() too. > { > + struct page *page; > unsigned long entry_offset = swp_offset(entry); > unsigned long offset = entry_offset; > unsigned long start_offset, end_offset; > @@ -668,11 +669,18 @@ struct page *swap_cluster_readahead(swp_entry_t entry, gfp_t gfp_mask, > end_offset = si->max - 1; > > blk_start_plug(&plug); > + /* If we read the page without waiting on IO, skip readahead. */ > + page = swap_cluster_read_one(entry, offset, gfp_mask, vma, addr, false); > + if (page && PageUptodate(page)) > + goto skip_unplug; > + > + /* Ok, do the async read-ahead now. */ > for (offset = start_offset; offset <= end_offset ; offset++) { > - /* Ok, do the async read-ahead now */ > - swap_cluster_read_one(entry, offset, gfp_mask, vma, addr, > - offset != entry_offset); > + if (offset == entry_offset) > + continue; > + swap_cluster_read_one(entry, offset, gfp_mask, vma, addr, true); > } > +skip_unplug: > blk_finish_plug(&plug); > > lru_add_drain(); /* Push any new pages onto the LRU now */ Best Regards, Huang, Ying