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/419564/ For those with LWN.net access, there is a detailed coverage of the patchset at http://lwn.net/Articles/419713/ The previous few revision received lot of comments, I've tried to address as many of those as possible in this revision. An earlier series was reviewed-by Christoph Lameter. There were comments on overlap with Nick's changes and overlap with them. I don't feel these changes impact Nick's work and integration can/will be considered as the patches evolve, if need be. 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. 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. Data from the previous patchsets can be found at https://lkml.org/lkml/2010/11/30/79 Size measurement CONFIG_UNMAPPED_PAGECACHE_CONTROL and CONFIG_NUMA enabled # size mm/built-in.o text data bss dec hex filename 419431 1883047 140888 2443366 254866 mm/built-in.o CONFIG_UNMAPPED_PAGECACHE_CONTROL disabled, CONFIG_NUMA enabled # size mm/built-in.o text data bss dec hex filename 418908 1883023 140888 2442819 254643 mm/built-in.o --- Balbir Singh (3): Move zone_reclaim() outside of CONFIG_NUMA Refactor zone_reclaim code Provide control over unmapped pages Documentation/kernel-parameters.txt | 8 ++ include/linux/mmzone.h | 4 + include/linux/swap.h | 21 +++++- init/Kconfig | 12 +++ kernel/sysctl.c | 20 +++-- mm/page_alloc.c | 9 ++ mm/vmscan.c | 132 +++++++++++++++++++++++++++++++---- 7 files changed, 175 insertions(+), 31 deletions(-) -- Balbir Singh -- 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
