On Wed, Sep 28, 2011 at 11:39 PM, Larry Bassel <lbassel@xxxxxxxxxxxxxx> wrote: > We need to create a large (~100M) contiguous physical memory region > which will only be needed occasionally. As this region will > use up 10-20% of all of the available memory, we do not want > to pre-reserve it at boot time. Instead, we want to create > this memory region "on the fly" when asked to by userspace, > and do it as quickly as possible, and return it to > system use when not needed. > > AFAIK, this sort of operation is currently done using memory > compaction (as CMA does for instance). > Alternatively, this memory region (if it is in a fixed place) > could be created using "logical memory hotremove" and returned > to the system using "logical memory hotplug". In either case, > the contiguous physical memory would be created via migrating > pages from the "movable zone". > > The problem with this approach is that the copying of up to 25000 > pages may take considerable time (as well as finding destinations > for all of the pages if free memory is scarce -- this may > even fail, causing the memory region not to be created). > > It was suggested to me that a new zone type which would be similar > to the "movable zone" but is only allowed to contain pages > that can be discarded (such as text) could solve this problem, > so that there is no copying or finding destination pages needed (thus > considerably reducing latency). > Is this approach similar to Copy-on-Write being used in most page sharing entitlements ? If yes, then it almost depends on the # of writes made on the pages. > The downside I see is that there may not be anywhere near > 25000 such discardable pages, so most of this zone would go unused, and > the memory would be "wasted" as in the case where it is pre-reserved. > Also, this is not currently supported, so new code would > have to be designed and implemented. > > I would appreciate people's comments about: > > 1. Does this type of zone make any sense? It > would have to co-exist with the current movable zone type. Ideally can't there be a reserved zone created from which all the remaining on-the fly zones are shared based on CoW ? > 2. How hard would it be to implement this? The new zone type would > need to be supported and "discardable" pages steered into this zone. > Most VMs do support ballooning, CoW and other forms of sharing and can provide as basis for any memory management projects. > 3. Are there better ways of allocating a large memory region > with minimal latency that I haven't mentioned here? > Hmm...there are mechanisms as pointed by yourself but they all depend on the policy of consolidation, priority and security of operations. > Thanks. > > Larry Bassel > > -- > Sent by an employee of the Qualcomm Innovation Center, Inc. > The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum. > > -- > To unsubscribe, send a message with 'unsubscribe linux-mm' in > the body to majordomo@xxxxxxxxx. For more info on Linux MM, > see: http://www.linux-mm.org/ . > Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ > Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a> > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href