* Balbir Singh <balbir@xxxxxxxxxxxxxxxxxx> [2010-06-08 21:21:46]: > Selectively control Unmapped Page Cache (nospam version) > > From: Balbir Singh <balbir@xxxxxxxxxxxxxxxxxx> > > This patch implements unmapped page cache control via preferred > page cache reclaim. The current patch hooks into kswapd and reclaims > page cache if the user has requested for unmapped page control. > This is useful in the following scenario > > - In a virtualized environment with cache=writethrough, we see > double caching - (one in the host and one in the guest). As > we try to scale guests, cache usage across the system grows. > The goal of this patch is to reclaim page cache when Linux is running > as a guest and get the host to hold the page cache and manage it. > There might be temporary duplication, but in the long run, memory > in the guests would be used for mapped pages. > - The option is controlled via a boot option and the administrator > can selectively turn it on, on a need to use basis. > > A lot of the code is borrowed from zone_reclaim_mode logic for > __zone_reclaim(). One might argue that the with ballooning and > KSM this feature is not very useful, but even with ballooning, > we need extra logic to balloon multiple VM machines and it is hard > to figure out the correct amount of memory to balloon. With these > patches applied, each guest has a sufficient amount of free memory > available, that can be easily seen and reclaimed by the balloon driver. > The additional memory in the guest can be reused for additional > applications or used to start additional guests/balance memory in > the host. > > KSM currently does not de-duplicate host and guest page cache. The goal > of this patch is to help automatically balance unmapped page cache when > instructed to do so. > > There are some magic numbers in use in the code, UNMAPPED_PAGE_RATIO > and the number of pages to reclaim when unmapped_page_control argument > is supplied. These numbers were chosen to avoid aggressiveness in > reaping page cache ever so frequently, at the same time providing control. > > The sysctl for min_unmapped_ratio provides further control from > within the guest on the amount of unmapped pages to reclaim. > Are there any major objections to this patch? -- Three Cheers, Balbir -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
