The following series implements page cache control, this is a split out version of patch 1 of version 3 of the page cache optimization patches posted earlier at Previous posting http://lwn.net/Articles/425851/ and analysis at http://lwn.net/Articles/419713/ Detailed Description ==================== 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. The sysctl for min_unmapped_ratio provides further control from within the guest on the amount of unmapped pages to reclaim, a similar max_unmapped_ratio sysctl is added and helps in the decision making process of when reclaim should occur. This is tunable and set by default to 16 (based on tradeoff's seen between aggressiveness in balancing versus size of unmapped pages). Distro's and administrators can further tweak this for desired control. Data from the previous patchsets can be found at https://lkml.org/lkml/2010/11/30/79 --- Balbir Singh (3): Move zone_reclaim() outside of CONFIG_NUMA Refactor zone_reclaim code Provide control over unmapped pages Documentation/kernel-parameters.txt | 8 ++ Documentation/sysctl/vm.txt | 19 +++++ include/linux/mmzone.h | 11 +++ include/linux/swap.h | 25 ++++++- init/Kconfig | 12 +++ kernel/sysctl.c | 29 ++++++-- mm/page_alloc.c | 35 +++++++++- mm/vmscan.c | 123 +++++++++++++++++++++++++++++++---- 8 files changed, 229 insertions(+), 33 deletions(-) -- 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
