On Thu, 2005-01-20 at 22:46 -0800, Andrew Morton wrote: > Nick Piggin <[EMAIL PROTECTED]> wrote:
> > It does turn on lowmem protection by default. We never reached > > an agreement about doing this though, but Andrea has shown that > > it fixes trivial OOM cases. > > > > I think it should be turned on by default. I can't recall what > > your reservations were...? > > > > Just that it throws away a bunch of potentially usable memory. In three > years I've seen zero reports of any problems which would have been solved > by increasing the protection ratio. > > Thus empirically, it appears that the number of machines which need a > non-zero protection ratio is exceedingly small. Why change the setting on > all machines for the benefit of the tiny few? Seems weird. Especially > when this problem could be solved with a few-line initscript. Ho hum. That is true, but it should not reserve a great deal of memory on small memory machines. ZONE_NORMAL reservation may not even be too noticeable as you'll usually have ZONE_NORMAL allocations during the course of normal running. Although it is true that there haven't been many problems attributed to this, one example I can remember is when we fixed the __alloc_pages watermark code, we fixed a bug that was reserving much more ZONE_DMA than it was supposed to. This cased all those page allocation failure problems. So we raised the atomic reserve, but that didn't bring ZONE_DMA reservation back to its previous levels. "So the buffer between GFP_KERNEL and GFP_ATOMIC allocations is: 2.6.8 | 465 dma, 117 norm, 582 tot = 2328K 2.6.10-rc | 2 dma, 146 norm, 148 tot = 592K patch | 12 dma, 500 norm, 512 tot = 2048K" So we were still seeing GFP_DMA allocation failures in the sound code. You recently had to make that NOWARN to shut it up. OK this is a fairly lame example... but the current code is more or less just lucky that ZONE_DMA doesn't usually fill up with pinned mem on machines that need explicit ZONE_DMA allocations. Find local movie times and trailers on Yahoo! Movies. http://au.movies.yahoo.com - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
