|From:||David Howells <firstname.lastname@example.org>|
|Subject:||[PATCH 00/43] Permit filesystem local caching [ver #46]|
|Date:||Thu, 02 Apr 2009 00:03:21 +0100|
|Cc:||email@example.com, firstname.lastname@example.org, email@example.com, firstname.lastname@example.org|
These patches add local caching for network filesystems such as NFS. To give a really quick overview of the way the facility works: +---------+ | | | NFS |--+ | | | +---------+ | +----------+ | | | +---------+ +-->| | | | | | | AFS |----->| FS-Cache | | | | |--+ +---------+ +-->| | | | | | | +--------------+ +--------------+ +---------+ | +----------+ | | | | | | | | +-->| CacheFiles |-->| Ext3 | | ISOFS |--+ | /var/cache | | /dev/sda6 | | | +--------------+ +--------------+ +---------+ (1) NFS, say, asks FS-Cache to store/retrieve data for it; (2) FS-Cache asks the cache backend, in this case CacheFiles to honour the operation; (3) CacheFiles 'opens' a file in a mounted filesystem, say Ext3, and does read and write operations of a sort on it; (4) Ext3 decides how the cache data is laid out on disk - CacheFiles just attempts to use one sparse file per netfs inode. (5) If NFS asks for data from the cache, but the file has a hole in it, NFS falls back to asking the server. The data obtained from the server is then written over the hole in the file. To look at it another way: +---------+ | | | Server | | | +---------+ | NETWORK ~~~~~|~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | | +----------+ V | | +---------+ | | | | | | | NFS |----->| FS-Cache | | | | |--+ +---------+ | | | +--------------+ +--------------+ | | | | | | | | V +----------+ +-->| CacheFiles |-->| Ext3 | +---------+ | /var/cache | | /dev/sda6 | | | +--------------+ +--------------+ | VFS | ^ ^ | | | | +---------+ +--------------+ | | KERNEL SPACE | | ~~~~~|~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~|~~~~~~|~~~~ | USER SPACE | | V | | +---------+ +--------------+ | | | | | Process | | cachefilesd | | | | | +---------+ +--------------+ FS-Cache attempts to provide a caching facility to a network filesystem such that it's transparent to the users of that network filesystem. The patches can roughly be broken down into a number of sets: (*) 01-slow-work.diff (*) 02-slow-work-dynamic.diff (*) 03-slow-work-config.diff (*) 04-slow-work-doc.diff A thread pool for (very) slow work items, such as batches of lookup, mkdir, create and [sg]etxattr calls. It doesn't make sense to use an ordinary work queue because I want more than one thread, but I don't want to be limited to 1 thread per CPU. The work items in question take a long time, most of which is spent sleeping on I/O. For the duration the worker thread is unable to do anything else. These four patches add the basic facility, make it dynamic, make it configurable and document it. (*) 05-release-page.diff Call the page release function after a failed readahead. (*) 06-fscache-page-flags.diff Add two extra page flags that FS-Cache then uses to keep track of two bits of per-cached-page information: (1) This page is known by the cache, and that the cache must be informed if the page is going to go away. It's an indication to the netfs that the cache has an interest in this page, where an interest may be a pointer to it, resources allocated or reserved for it, or I/O in progress upon it. (2) This page is being written to disk by the cache, and that it cannot be released until completion. Ideally it shouldn't be changed until completion either so as to maintain the known state of the cache. This cannot be unified with PG_writeback as the page may be being written to both the server and the cache at the same time or at different times. To avoid using extra page bits, I could, for example, set up a radix tree per data storage object to keep track of both these bits, however this would mean that the netfs would have to do a call, spinlock, conditional jumps, etc to find out either state. On the other hand, if we can spare two page flags, those are sufficient. Note that the cache doesn't necessarily need to be able to find the netfs pages, but may have to allocate/pin resources for backing them. Further note that PG_private may not be used as I want to be able to use caching with ISOFS eventually, and PG_private is owned by the block buffer code. These bits can be otherwise used by any filesystem that doesn't want to use FS-Cache. (*) 07-fscache-netfs-api.diff (*) 08-fscache-backend-api.diff (*) 09-fscache-kconfig.diff (*) 10-fscache-proc.diff (*) 11-fscache-fsdef.diff (*) 12-fscache-tag-handling.diff (*) 13-fscache-cache-handling.diff (*) 14-fscache-cookie-jar.diff (*) 15-fscache-netfs-reg.diff (*) 16-fscache-bits.diff (*) 17-fscache-object.diff (*) 18-fscache-cookie.diff (*) 19-fscache-operation.diff (*) 20-fscache-io.diff Patches to provide a local caching facility for network filesystems. FS-Cache is a layer that takes requests from any one of a number of netfs's and passes them to an appropriate cache, if there is one. FS-Cache makes operations requested by the netfs transparently asynchronous where possible. FS-Cache also protects the netfs against (a) there being no cache, (b) the cache suffering a fatal I/O error and (c) the cache being removed; and protects the cache against (d) the netfs uncaching pages that the cache is using and (e) conflicting operations from the netfs, some of which may be queued for asynchronous processing. Five documents in text file format that describe the FS-Cache interface are added by these patches: Documentation/filesystems/caching/fscache.txt gives an overview of the facility and describes the statistical data it makes available. Documentation/filesystems/caching/netfs-api.txt describes the API by which a network filesystem would make use of the FS-Cache facility. Documentation/filesystems/caching/backend-api.txt describes the API that a cache backend must implement to provide caching services through FS-Cache. Documentation/filesystems/caching/object.txt describes the object management state machine used. Documentation/filesystems/caching/operations.txt describes the operation scheduling facility provided and used by FS-Cache that can also be used by cache backend modules. The patches provide the following components of the FS-Cache facility: (07) The netfs API header file and documentation. A netfs can actually be built and run against just this patch. It won't actually do anything without the later patches, though, but it will compile. (08) The cache backend API header file and documentation. (09) The main selector configuration option, the main module load/unload hooks and the debugging code declarations. With this patch applied, it is possible to enable caching in a client netfs, though it won't actually do anything. (10) The /proc files for statistics presentation, plus the internal interfaces for driving it. (11) The top level index definition. (12) Cache reference tag handling. (13) Cache (un)registration and error handling. (14) Cookie (de)allocator and initialisation. (15) Netfs (un)registration handling. This is partly usable. Without a later patch, however, a cookie will be leaked from unregistration. (16) Bit waiting utility functions. (17) The object management state machine implementation and documentation. (18) Implementation of the cookie management part of the netfs API. With this, it's possible for netfs's to actually be granted cookies and to release them without error. (19) Cache I/O operation scheduler and documentation. (20) Implementation of the data I/O part of the netfs API. (*) 21-cachefiles-ext3-f_mapping.diff (*) 22-cachefiles-write.diff (*) 23-cachefiles-monitor.diff (*) 24-cachefiles-export.diff (*) 25-cachefiles.diff Patches to provide a local cache in a directory of an already mounted filesystem. The latter patch adds a document in text file format that describes the CacheFiles cache backend and gives instructions on how it is set up and used. This will be Documentation/filesystems/caching/cachefiles.txt when the patch is applied. (*) 26-afs-fscache.diff Patches to provide AFS with local caching. (*) 27-nfs-comment.diff (*) 28-nfs-fscache-option.diff (*) 29-nfs-fscache-kconfig.diff (*) 30-nfs-fscache-top-index.diff (*) 31-nfs-fscache-server-obj.diff (*) 32-nfs-fscache-super-obj.diff (*) 33-nfs-fscache-inode-obj.diff (*) 34-nfs-fscache-use-inode.diff (*) 35-nfs-fscache-invalidate-pages.diff (*) 36-nfs-fscache-iostats.diff (*) 37-nfs-fscache-page-management.diff (*) 38-nfs-fscache-read-context.diff (*) 39-nfs-fscache-read-fallback.diff (*) 40-nfs-fscache-read-from-cache.diff (*) 41-nfs-fscache-store-to-cache.diff (*) 42-nfs-fscache-display.diff (*) 43-nfs-fscache-mount.diff Patches to provide NFS with local caching. I've renamed the files in fs/fscache/ from fsc-XXX to XXX, and similarly the files called cf-XXX to XXX in fs/cachefiles/. I've also fixed some minor conflicts with NFS changes that have gone in to Linus's tree. I've been testing these patches by throwing batches of eight parallel "tar cf" commands across three different 350MB NFS-based kernel trees (3 tars on first tree, 3 on second, 2 on third), sometimes with one or more of the trees preloaded into the cache. The complete working data set does not fit into the RAM of my test machine, so even three tars that can be entirely satisfied from the cache may have to reread everything from disk. I've also been running tars against AFS mounted kernel trees. -- A tarball of the patches is available at: http://people.redhat.com/~dhowells/fscache/patches/nfs+fs... This builds on top of Linus's current kernel. The code can also be obtained by GIT from: git://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-2.6-fscache.git http://www.kernel.org/pub/scm/linux/kernel/git/dhowells/l... tagged as 'fscache-46'. To use this version of CacheFiles, the cachefilesd-0.9 is also required. It is available as an SRPM: http://people.redhat.com/~dhowells/fscache/cachefilesd-0.... Or as individual bits: http://people.redhat.com/~dhowells/fscache/cachefilesd-0.... http://people.redhat.com/~dhowells/fscache/cachefilesd.fc http://people.redhat.com/~dhowells/fscache/cachefilesd.if http://people.redhat.com/~dhowells/fscache/cachefilesd.te http://people.redhat.com/~dhowells/fscache/cachefilesd.spec The .fc, .if and .te files are for manipulating SELinux. David -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to email@example.com More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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