V15->V16 - Reworked core logic against 4.11 kernel code - Just the bare bones for Matthew to have the ability to review the patches and to see how slab defrag could work with the radix tree and/or new xarrays. Skip reclaim integration etc etc. V14->V15 - The lost version ... I posted it in 2010 but the material is nowhere to be found on my backups. V13->V14 - Rediff against linux-next on request of Andrew - TestSetPageLocked -> trylock_page conversion. Slab fragmentation is mainly an issue if Linux is used as a fileserver and large amounts of dentries, inodes and buffer heads accumulate. In some load situations the slabs become very sparsely populated so that a lot of memory is wasted by slabs that only contain one or a few objects. In extreme cases the performance of a machine will become sluggish since we are continually running reclaim without much succes. Slab defragmentation adds the capability to recover the memory that is wasted. Memory reclaim for the following slab caches is possible: 1. dentry cache 2. inode cache (with a generic interface to allow easy setup of more filesystems than the currently supported ext2/3/4 reiserfs, XFS and proc) 3. buffer_heads One typical mechanism that triggers slab defragmentation on my systems is the daily run of updatedb Updatedb scans all files on the system which causes a high inode and dentry use. After updatedb is complete we need to go back to the regular use patterns (typical on my machine: kernel compiles). Those need the memory now for different purposes. The inodes and dentries used for updatedb will gradually be aged by the dentry/inode reclaim algorithm which will free up the dentries and inode entries randomly through the slabs that were allocated. As a result the slabs will become sparsely populated. If they become empty then they can be freed but a lot of them will remain sparsely populated. That is where slab defrag comes in: It removes the objects from the slabs with just a few entries reclaiming more memory for other uses. In the simplest case (as provided here) this is done by simply reclaiming the objects. However, if the logic in the kick() function is made more sophisticated then we will be able to move the objects out of the slabs. Allocations of objects is possible if a slab is fragmented without the use of the page allocator because a large number of free slots are available. Moving an object will reduce fragmentation in the slab the object is moved to. V12->v13: - Rebase onto Linux 2.6.27-rc1 (deal with page flags conversion, ctor parameters etc) - Fix unitialized variable issue V11->V12: - Pekka and me fixed various minor issues pointed out by Andrew. - Split ext2/3/4 defrag support patches. - Add more documentation - Revise the way that slab defrag is triggered from reclaim. No longer use a timeout but track the amount of slab reclaim done by the shrinkers. Add a field in /proc/sys/vm/slab_defrag_limit to control the threshold. - Display current slab_defrag_counters in /proc/zoneinfo (for a zone) and /proc/sys/vm/slab_defrag_count (for global reclaim). - Add new config vaue slab_defrag_limit to /proc/sys/vm/slab_defrag_limit - Add a patch that obsoletes SLAB and explains why SLOB does not support defrag (Either of those could be theoretically equipped to support slab defrag in some way but it seems that Andrew/Linus want to reduce the number of slab allocators). V10->V11 - Simplify determination when to reclaim: Just scan over all partials and check if they are sparsely populated. - Add support for performance counters - Rediff on top of current slab-mm. - Reduce frequency of scanning. A look at the stats showed that we were calling into reclaim very frequently when the system was under memory pressure which slowed things down. Various measures to avoid scanning the partial list too frequently were added and the earlier (expensive) method of determining the defrag ratio of the slab cache as a whole was dropped. I think this addresses the issues that Mel saw with V10. V9->V10 - Rediff against upstream V8->V9 - Rediff against 2.6.24-rc6-mm1 V7->V8 - Rediff against 2.6.24-rc3-mm2 V6->V7 - Rediff against 2.6.24-rc2-mm1 - Remove lumpy reclaim support. No point anymore given that the antifrag handling in 2.6.24-rc2 puts reclaimable slabs into different sections. Targeted reclaim never triggers. This has to wait until we make slabs movable or we need to perform a special version of lumpy reclaim in SLUB while we scan the partial lists for slabs to kick out. Removal simplifies handling significantly since we get to slabs in a more controlled way via the partial lists. The patchset now provides pure reduction of fragmentation levels. - SLAB/SLOB: Provide inlines that do nothing - Fix various smaller issues that were brought up during review of V6. V5->V6 - Rediff against 2.6.24-rc2 + mm slub patches. - Add reviewed by lines. - Take out the experimental code to make slab pages movable. That has to wait until this has been considered by Mel. V4->V5: - Support lumpy reclaim for slabs - Support reclaim via slab_shrink() - Add constructors to insure a consistent object state at all times. V3->V4: - Optimize scan for slabs that need defragmentation - Add /sys/slab/*/defrag_ratio to allow setting defrag limits per slab. - Add support for buffer heads. - Describe how the cleanup after the daily updatedb can be improved by slab defragmentation. V2->V3 - Support directory reclaim - Add infrastructure to trigger defragmentation after slab shrinking if we have slabs with a high degree of fragmentation. V1->V2 - Clean up control flow using a state variable. Simplify API. Back to 2 functions that now take arrays of objects. - Inode defrag support for a set of filesystems - Fix up dentry defrag support to work on negative dentries by adding a new dentry flag that indicates that a dentry is not in the process of being freed or allocated. -- 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/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
