From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Tue, 31 Jul 2007 16:09:43 -0700 From: Andrew Morton Subject: Re: make swappiness safer to use Message-Id: <20070731160943.30e9c13a.akpm@linux-foundation.org> In-Reply-To: <20070731215228.GU6910@v2.random> References: <20070731215228.GU6910@v2.random> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Andrea Arcangeli Cc: linux-mm@kvack.org, Nick Piggin , Martin Bligh List-ID: On Tue, 31 Jul 2007 23:52:28 +0200 Andrea Arcangeli wrote: > I think the prev_priority can also be nuked since it wastes 4 bytes > per zone (that would be an incremental patch but I wait the > nr_scan_[in]active to be nuked first for similar reasons). Clearly > somebody at some point noticed how broken that thing was and they had > to add min(priority, prev_priority) to give it some reliability, but > they didn't go the last mile to nuke prev_priority too. Calculating > distress only in function of not-racy priority is correct and sure > more than enough without having to add randomness into the equation. I don't recall seeing any such patch and I suspect it'd cause problems anyway. If we were to base swap_tendency purely on sc->priority then the VM would incorrectly fail to deactivate mapped pages until the scanning had reached a sufficiently high (ie: low) scanning priority. The net effect would be that each time some process runs shrink_active_list(), some pages would be incorrectly retained on the active list and after a while, the code wold start moving mapped pages down to the inactive list. In fact, I think that was (effectively) the behaviour which we had in there, and it caused problems with some worklaod which Martin was looking at and things got better when we fixed it. Anyway, we can say more if we see the patch (or, more accurately, the analysis which comes with that patch). -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org