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Date: Wed, 18 Oct 2006 03:14:58 +1000 From: Nick Piggin <nickpiggin@...oo.com.au> To: Martin Bligh <mbligh@...gle.com> CC: Andrew Morton <akpm@...l.org>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, Linux Memory Management <linux-mm@...ck.org> Subject: Re: [PATCH] Use min of two prio settings in calculating distress for reclaim Martin Bligh wrote: >> Distress is a per-zone thing. It is precisely that way because there >> *are* >> different types of reclaim and you don't want a crippled reclaimer (which >> might indeed be having trouble reclaiming stuff) from saying the system >> is in distress. >> >> If they are the *only* reclaimer, then OK, distress will go up. > > > So you'd rather the "crippled" reclaimer went and fire the OOM killer > and shoot someone instead? No, so I fixed that. http://www.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=408d85441cd5a9bd6bc851d677a10c605ed8db5f > I don't see why we should penalise them, > especially as the dirty page throttling is global, and will just kick > pretty much anyone trying to do an allocation. There's nothing magic How does dirty page throttling kick anyone trying to do an allocation? It kicks at page dirtying time. > about the "crippled" reclaimer as you put it. They're doing absolutely > nothing wrong, or that they should be punished for. They need a page. When did I say anything about magic or being punished? They need a page and they will get it when enough memory gets freed. Pages being reclaimed by process A may be allocated by process B just fine. >> I don't agree that the thing to aim for is ensuring everyone is able >> to reclaim something. >> >> And why do you ignore the other side of the coin, where now reclaimers >> that are easily able to make progress are being made to swap stuff out? > > > Because I'd rather err on the side of moving a few mapped pages from the > active to the inactive list than cause massive latencies for a page > allocation that's dropping into direct reclaim and/or going OOM. We shouldn't go OOM. And there are latencies everywhere and this won't fix them. A GFP_NOIO allocator can't swap out pages at all, for example. >> If the GFP_NOFS reclaimer is having a lot of trouble reclaiming, and so >> you decide to turn on reclaim_mapped, then it is not suddenly going to >> be able to free those pages. > > > Well it's certainly not going to work if we don't even try. There were > ZERO pages in the inactive list at this point. The system is totally > frigging hosed and we're not even trying to reclaim pages because > we're in deluded-happy-la-la land and we think everything is fine. So that could be the temp_priority race. If no progress is being made anywhere, the current logic (minus races) says that prev_prio should reach 0. Regardless of whether it is GFP_NOFS or whatever. > This is what happens as we kick down prio levels in one thread: > > priority = 12 active_distress = 0 swap_tendency = 0 gfp_mask = d0 > priority = 12 active_distress = 0 swap_tendency = 0 gfp_mask = d0 > priority = 11 active_distress = 25 swap_tendency = 106 gfp_mask = d0 > priority = 10 active_distress = 25 swap_tendency = 106 gfp_mask = d0 > priority = 9 active_distress = 0 swap_tendency = 81 gfp_mask = d0 > priority = 8 active_distress = 0 swap_tendency = 81 gfp_mask = d0 > priority = 7 active_distress = 25 swap_tendency = 106 gfp_mask = d0 > priority = 6 active_distress = 25 swap_tendency = 106 gfp_mask = d0 > priority = 5 active_distress = 25 swap_tendency = 106 gfp_mask = d0 > priority = 4 active_distress = 25 swap_tendency = 106 gfp_mask = d0 > priority = 3 active_distress = 25 swap_tendency = 106 gfp_mask = d0 > priority = 2 active_distress = 50 swap_tendency = 131 gfp_mask = d0 > priority = 1 active_distress = 0 swap_tendency = 81 gfp_mask = d0 > priority = 0 active_distress = 0 swap_tendency = 81 gfp_mask = d0 > > Notice that distress is not kicking up as priority kicks down (see > 1 and 0 at the end). Because some other idiot reset prev_priority > back to 12. Fine, so fix that race rather than papering over it by using the min of prev_priority and current priority. -- SUSE Labs, Novell Inc. Send instant messages to your online friends http://au.messenger.yahoo.com - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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