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Date: Mon, 13 Apr 2020 21:13:33 +0800 From: "Huang\, Ying" <ying.huang@...el.com> To: Andrea Righi <andrea.righi@...onical.com> Cc: Andrew Morton <akpm@...ux-foundation.org>, Minchan Kim <minchan@...nel.org>, Anchal Agarwal <anchalag@...zon.com>, <linux-mm@...ck.org>, <linux-kernel@...r.kernel.org> Subject: Re: [PATCH v2] mm: swap: use fixed-size readahead during swapoff Andrea Righi <andrea.righi@...onical.com> writes: > The global swap-in readahead policy takes in account the previous access > patterns, using a scaling heuristic to determine the optimal readahead > chunk dynamically. > > This works pretty well in most cases, but like any heuristic there are > specific cases when this approach is not ideal, for example the swapoff > scenario. > > During swapoff we just want to load back into memory all the swapped-out > pages and for this specific use case a fixed-size readahead is more > efficient. > > The specific use case this patch is addressing is to improve swapoff > performance when a VM has been hibernated, resumed and all memory needs > to be forced back to RAM by disabling swap (see the test case below). Why do you need to swapoff after resuming? The swap device isn't used except hibernation? I guess the process is, 1) add swap device to VM 2) hibernate 3) resume 4) swapoff Some pages are swapped out in step 2? If os, can we just set /proc/sys/vm/swappiness to 0 to avoid swapping in step 2? Best Regards, Huang, Ying
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