Messages in this thread | | | Date | Wed, 11 Jan 2012 16:58:14 -0500 | From | Rik van Riel <> | Subject | Re: [PATCH v2 -mm] make swapin readahead skip over holes |
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On 01/11/2012 04:42 PM, Johannes Weiner wrote: > On Wed, Jan 11, 2012 at 04:30:12PM -0500, Rik van Riel wrote: >> On 01/11/2012 04:10 PM, Johannes Weiner wrote: >>> On Wed, Jan 11, 2012 at 02:30:44PM -0500, Rik van Riel wrote: >>>> Ever since abandoning the virtual scan of processes, for scalability >>>> reasons, swap space has been a little more fragmented than before. >>>> This can lead to the situation where a large memory user is killed, >>>> swap space ends up full of "holes" and swapin readahead is totally >>>> ineffective. >>>> >>>> On my home system, after killing a leaky firefox it took over an >>>> hour to page just under 2GB of memory back in, slowing the virtual >>>> machines down to a crawl. >>>> >>>> This patch makes swapin readahead simply skip over holes, instead >>>> of stopping at them. This allows the system to swap things back in >>>> at rates of several MB/second, instead of a few hundred kB/second. >>>> >>>> The checks done in valid_swaphandles are already done in >>>> read_swap_cache_async as well, allowing us to remove a fair amount >>>> of code. >>> >>> __swap_duplicate() also checks for whether the offset is within the >>> swap device range. Do you think we could remove get_swap_cluster() >>> altogether and just try reading the aligned page_cluster range? >> >> That is how I implemented it originally, but we need >> to take the swap_lock so it is cleaner to implement >> a helper function in swapfile.c :) > > AFAICS, it's only needed to validate the offset against si->max, but > this too is done in __swap_duplicate(). > > What's otherwise left is just rounding down swp_offset(entry) and > adding 1<< page_cluster to it, that shouldn't need the swap_lock? > > Am I missing something?
Good point. I guess we could get rid of get_swap_cluster afterall and let __swap_duplicate deal with everything.
Andrew, Mel, is that ok with you?
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