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* readahead: remove the old algorithmFengguang Wu2007-07-191-348/+25
| | | | | | | | | | | Remove the old readahead algorithm. Signed-off-by: Fengguang Wu <wfg@mail.ustc.edu.cn> Cc: Steven Pratt <slpratt@austin.ibm.com> Cc: Ram Pai <linuxram@us.ibm.com> Cc: Rusty Russell <rusty@rustcorp.com.au> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* readahead: on-demand readahead logicFengguang Wu2007-07-191-0/+174
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | This is a minimal readahead algorithm that aims to replace the current one. It is more flexible and reliable, while maintaining almost the same behavior and performance. Also it is full integrated with adaptive readahead. It is designed to be called on demand: - on a missing page, to do synchronous readahead - on a lookahead page, to do asynchronous readahead In this way it eliminated the awkward workarounds for cache hit/miss, readahead thrashing, retried read, and unaligned read. It also adopts the data structure introduced by adaptive readahead, parameterizes readahead pipelining with `lookahead_index', and reduces the current/ahead windows to one single window. HEURISTICS The logic deals with four cases: - sequential-next found a consistent readahead window, so push it forward - random standalone small read, so read as is - sequential-first create a new readahead window for a sequential/oversize request - lookahead-clueless hit a lookahead page not associated with the readahead window, so create a new readahead window and ramp it up In each case, three parameters are determined: - readahead index: where the next readahead begins - readahead size: how much to readahead - lookahead size: when to do the next readahead (for pipelining) BEHAVIORS The old behaviors are maximally preserved for trivial sequential/random reads. Notable changes are: - It no longer imposes strict sequential checks. It might help some interleaved cases, and clustered random reads. It does introduce risks of a random lookahead hit triggering an unexpected readahead. But in general it is more likely to do good than to do evil. - Interleaved reads are supported in a minimal way. Their chances of being detected and proper handled are still low. - Readahead thrashings are better handled. The current readahead leads to tiny average I/O sizes, because it never turn back for the thrashed pages. They have to be fault in by do_generic_mapping_read() one by one. Whereas the on-demand readahead will redo readahead for them. OVERHEADS The new code reduced the overheads of - excessively calling the readahead routine on small sized reads (the current readahead code insists on seeing all requests) - doing a lot of pointless page-cache lookups for small cached files (the current readahead only turns itself off after 256 cache hits, unfortunately most files are < 1MB, so never see that chance) That accounts for speedup of - 0.3% on 1-page sequential reads on sparse file - 1.2% on 1-page cache hot sequential reads - 3.2% on 256-page cache hot sequential reads - 1.3% on cache hot `tar /lib` However, it does introduce one extra page-cache lookup per cache miss, which impacts random reads slightly. That's 1% overheads for 1-page random reads on sparse file. PERFORMANCE The basic benchmark setup is - 2.6.20 kernel with on-demand readahead - 1MB max readahead size - 2.9GHz Intel Core 2 CPU - 2GB memory - 160G/8M Hitachi SATA II 7200 RPM disk The benchmarks show that - it maintains the same performance for trivial sequential/random reads - sysbench/OLTP performance on MySQL gains up to 8% - performance on readahead thrashing gains up to 3 times iozone throughput (KB/s): roughly the same ========================================== iozone -c -t1 -s 4096m -r 64k 2.6.20 on-demand gain first run " Initial write " 61437.27 64521.53 +5.0% " Rewrite " 47893.02 48335.20 +0.9% " Read " 62111.84 62141.49 +0.0% " Re-read " 62242.66 62193.17 -0.1% " Reverse Read " 50031.46 49989.79 -0.1% " Stride read " 8657.61 8652.81 -0.1% " Random read " 13914.28 13898.23 -0.1% " Mixed workload " 19069.27 19033.32 -0.2% " Random write " 14849.80 14104.38 -5.0% " Pwrite " 62955.30 65701.57 +4.4% " Pread " 62209.99 62256.26 +0.1% second run " Initial write " 60810.31 66258.69 +9.0% " Rewrite " 49373.89 57833.66 +17.1% " Read " 62059.39 62251.28 +0.3% " Re-read " 62264.32 62256.82 -0.0% " Reverse Read " 49970.96 50565.72 +1.2% " Stride read " 8654.81 8638.45 -0.2% " Random read " 13901.44 13949.91 +0.3% " Mixed workload " 19041.32 19092.04 +0.3% " Random write " 14019.99 14161.72 +1.0% " Pwrite " 64121.67 68224.17 +6.4% " Pread " 62225.08 62274.28 +0.1% In summary, writes are unstable, reads are pretty close on average: access pattern 2.6.20 on-demand gain Read 62085.61 62196.38 +0.2% Re-read 62253.49 62224.99 -0.0% Reverse Read 50001.21 50277.75 +0.6% Stride read 8656.21 8645.63 -0.1% Random read 13907.86 13924.07 +0.1% Mixed workload 19055.29 19062.68 +0.0% Pread 62217.53 62265.27 +0.1% aio-stress: roughly the same ============================ aio-stress -l -s4096 -r128 -t1 -o1 knoppix511-dvd-cn.iso aio-stress -l -s4096 -r128 -t1 -o3 knoppix511-dvd-cn.iso 2.6.20 on-demand delta sequential 92.57s 92.54s -0.0% random 311.87s 312.15s +0.1% sysbench fileio: roughly the same ================================= sysbench --test=fileio --file-io-mode=async --file-test-mode=rndrw \ --file-total-size=4G --file-block-size=64K \ --num-threads=001 --max-requests=10000 --max-time=900 run threads 2.6.20 on-demand delta first run 1 59.1974s 59.2262s +0.0% 2 58.0575s 58.2269s +0.3% 4 48.0545s 47.1164s -2.0% 8 41.0684s 41.2229s +0.4% 16 35.8817s 36.4448s +1.6% 32 32.6614s 32.8240s +0.5% 64 23.7601s 24.1481s +1.6% 128 24.3719s 23.8225s -2.3% 256 23.2366s 22.0488s -5.1% second run 1 59.6720s 59.5671s -0.2% 8 41.5158s 41.9541s +1.1% 64 25.0200s 23.9634s -4.2% 256 22.5491s 20.9486s -7.1% Note that the numbers are not very stable because of the writes. The overall performance is close when we sum all seconds up: sum all up 495.046s 491.514s -0.7% sysbench oltp (trans/sec): up to 8% gain ======================================== sysbench --test=oltp --oltp-table-size=10000000 --oltp-read-only \ --mysql-socket=/var/run/mysqld/mysqld.sock \ --mysql-user=root --mysql-password=readahead \ --num-threads=064 --max-requests=10000 --max-time=900 run 10000-transactions run threads 2.6.20 on-demand gain 1 62.81 64.56 +2.8% 2 67.97 70.93 +4.4% 4 81.81 85.87 +5.0% 8 94.60 97.89 +3.5% 16 99.07 104.68 +5.7% 32 95.93 104.28 +8.7% 64 96.48 103.68 +7.5% 5000-transactions run 1 48.21 48.65 +0.9% 8 68.60 70.19 +2.3% 64 70.57 74.72 +5.9% 2000-transactions run 1 37.57 38.04 +1.3% 2 38.43 38.99 +1.5% 4 45.39 46.45 +2.3% 8 51.64 52.36 +1.4% 16 54.39 55.18 +1.5% 32 52.13 54.49 +4.5% 64 54.13 54.61 +0.9% That's interesting results. Some investigations show that - MySQL is accessing the db file non-uniformly: some parts are more hot than others - It is mostly doing 4-page random reads, and sometimes doing two reads in a row, the latter one triggers a 16-page readahead. - The on-demand readahead leaves many lookahead pages (flagged PG_readahead) there. Many of them will be hit, and trigger more readahead pages. Which might save more seeks. - Naturally, the readahead windows tend to lie in hot areas, and the lookahead pages in hot areas is more likely to be hit. - The more overall read density, the more possible gain. That also explains the adaptive readahead tricks for clustered random reads. readahead thrashing: 3 times better =================================== We boot kernel with "mem=128m single", and start a 100KB/s stream on every second, until reaching 200 streams. max throughput min avg I/O size 2.6.20: 5MB/s 16KB on-demand: 15MB/s 140KB Signed-off-by: Fengguang Wu <wfg@mail.ustc.edu.cn> Cc: Steven Pratt <slpratt@austin.ibm.com> Cc: Ram Pai <linuxram@us.ibm.com> Cc: Rusty Russell <rusty@rustcorp.com.au> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* readahead: data structure and routinesFengguang Wu2007-07-191-0/+19
| | | | | | | | | | | | Extend struct file_ra_state to support the on-demand readahead logic. Also define some helpers for it. Signed-off-by: Fengguang Wu <wfg@mail.ustc.edu.cn> Cc: Steven Pratt <slpratt@austin.ibm.com> Cc: Ram Pai <linuxram@us.ibm.com> Cc: Rusty Russell <rusty@rustcorp.com.au> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* readahead: MIN_RA_PAGES/MAX_RA_PAGES macrosFengguang Wu2007-07-191-2/+10
| | | | | | | | | | | | | | | | | Define two convenient macros for read-ahead: - MAX_RA_PAGES: rounded down counterpart of VM_MAX_READAHEAD - MIN_RA_PAGES: rounded _up_ counterpart of VM_MIN_READAHEAD Note that the rounded up MIN_RA_PAGES will work flawlessly with _large_ page sizes like 64k. Signed-off-by: Fengguang Wu <wfg@mail.ustc.edu.cn> Cc: Steven Pratt <slpratt@austin.ibm.com> Cc: Ram Pai <linuxram@us.ibm.com> Cc: Rusty Russell <rusty@rustcorp.com.au> Cc: <stable@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* readahead: add look-ahead support to __do_page_cache_readahead()Fengguang Wu2007-07-191-6/+9
| | | | | | | | | | | | | | | | | | | | | | | Add look-ahead support to __do_page_cache_readahead(). It works by - mark the Nth backwards page with PG_readahead, (which instructs the page's first reader to invoke readahead) - and only do the marking for newly allocated pages. (to prevent blindly doing readahead on already cached pages) Look-ahead is a technique to achieve I/O pipelining: While the application is working through a chunk of cached pages, the kernel reads-ahead the next chunk of pages _before_ time of need. It effectively hides low level I/O latencies to high level applications. Signed-off-by: Fengguang Wu <wfg@mail.ustc.edu.cn> Cc: Steven Pratt <slpratt@austin.ibm.com> Cc: Ram Pai <linuxram@us.ibm.com> Cc: Rusty Russell <rusty@rustcorp.com.au> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* readahead: code cleanupJan Kara2007-05-071-15/+15
| | | | | | | | | | | | | | Rename file_ra_state.prev_page to prev_index and file_ra_state.offset to prev_offset. Also update of prev_index in do_generic_mapping_read() is now moved close to the update of prev_offset. [wfg@mail.ustc.edu.cn: fix it] Signed-off-by: Jan Kara <jack@suse.cz> Cc: Nick Piggin <nickpiggin@yahoo.com.au> Cc: WU Fengguang <wfg@mail.ustc.edu.cn> Signed-off-by: Fengguang Wu <wfg@mail.ustc.edu.cn> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* readahead: improve heuristic detecting sequential readsJan Kara2007-05-071-0/+3
| | | | | | | | | | | | | | Introduce ra.offset and store in it an offset where the previous read ended. This way we can detect whether reads are really sequential (and thus we should not mark the page as accessed repeatedly) or whether they are random and just happen to be in the same page (and the page should really be marked accessed again). Signed-off-by: Jan Kara <jack@suse.cz> Acked-by: Nick Piggin <nickpiggin@yahoo.com.au> Cc: WU Fengguang <wfg@mail.ustc.edu.cn> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* [PATCH] Drop __get_zone_counts()Christoph Lameter2007-02-111-6/+2
| | | | | | | | Values are readily available via ZVC per node and global sums. Signed-off-by: Christoph Lameter <clameter@sgi.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* [PATCH] io-accounting-read-accounting nfs fixAndrew Morton2006-12-101-0/+2
| | | | | | | | | | | | | | | | nfs's ->readpages uses read_cache_pages(). Wire it up there. [wfg@mail.ustc.edu.cn: account only successful nfs/fuse reads] Cc: Jay Lan <jlan@sgi.com> Cc: Shailabh Nagar <nagar@watson.ibm.com> Cc: Balbir Singh <balbir@in.ibm.com> Cc: Chris Sturtivant <csturtiv@sgi.com> Cc: Tony Ernst <tee@sgi.com> Cc: Guillaume Thouvenin <guillaume.thouvenin@bull.net> Cc: David Wright <daw@sgi.com> Signed-off-by: Fengguang Wu <wfg@mail.ustc.edu.cn> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
* [PATCH] struct path: convert mmJosef Sipek2006-12-081-1/+1
| | | | | | Signed-off-by: Josef Sipek <jsipek@fsl.cs.sunysb.edu> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
* [PATCH] read_cache_pages() cleanupOGAWA Hirofumi2006-12-071-7/+1
| | | | | | | | Use put_pages_list() instead of opencoding it. Signed-off-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
* [PATCH] Cleanup read_pages()OGAWA Hirofumi2006-11-031-0/+2
| | | | | | | | | | | | | | | | Current read_pages() assume ->readpages() frees the passed pages. This patch free the pages in ->read_pages(), if those were remaining in the pages_list. So, readpages() just can ignore the remaining pages in pages_list. Signed-off-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp> Cc: Steven French <sfrench@us.ibm.com> Cc: Miklos Szeredi <miklos@szeredi.hu> Cc: Steven Whitehouse <swhiteho@redhat.com> Cc: Trond Myklebust <trond.myklebust@fys.uio.no> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
* Merge rsync://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux-2.6Steven Whitehouse2006-07-031-12/+8
|\ | | | | | | | | | | Conflicts: include/linux/kernel.h
| * spelling fixesAndreas Mohr2006-06-261-2/+2
| | | | | | | | | | | | | | | | | | | | | | | | acquired (aquired) contiguous (contigious) successful (succesful, succesfull) surprise (suprise) whether (weather) some other misspellings Signed-off-by: Andreas Mohr <andi@lisas.de> Signed-off-by: Adrian Bunk <bunk@stusta.de>
| * [PATCH] kernel-doc: mm/readhead fixupRandy Dunlap2006-06-251-2/+1
| | | | | | | | | | | | | | | | | | Put short function description for read_cache_pages() on one line as needed by kernel-doc. Signed-off-by: Randy Dunlap <rdunlap@xenotime.net> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
| * [PATCH] AOP_TRUNCATED_PAGE victims in read_pages() belong in the LRUZach Brown2006-06-251-8/+5
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | AOP_TRUNCATED_PAGE victims in read_pages() belong in the LRU Nick Piggin rightly pointed out that the introduction of AOP_TRUNCATED_PAGE to read_pages() was wrong to leave A_T_P victim pages in the page cache but not put them in the LRU. Failing to do so hid them from the VM. A_T_P just means that the aop method unlocked the page rather than performing IO. It would be very rare that the page was truncated between the unlock and testing A_T_P. So we leave the pages in the LRU for likely reuse soon rather than backing them back out of the page cache. We do this by matching the behaviour before the A_T_P introduction which added pages to the LRU regardless of what ->readpage() did. This doesn't include the unrelated cleanup in Nick's initial fix which changed read_pages() to return void to match its only caller's behaviour of ignoring errors. Signed-off-by: Nick Piggin <nickpiggin@yahoo.com.au> Signed-off-by: Zach Brown <zach.brown@oracle.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
* | Merge branch 'master'Steven Whitehouse2006-03-311-9/+24
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| * [PATCH] ext3_readdir: use generic readaheadAndrew Morton2006-03-231-0/+1
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Linus points out that ext3_readdir's readahead only cuts in when ext3_readdir() is operating at the very start of the directory. So for large directories we end up performing no readahead at all and we suck. So take it all out and use the core VM's page_cache_readahead(). This means that ext3 directory reads will use all of readahead's dynamic sizing goop. Note that we're using the directory's filp->f_ra to hold the readahead state, but readahead is actually being performed against the underlying blockdev's address_space. Fortunately the readahead code is all set up to handle this. Tested with printk. It works. I was struggling to find a real workload which actually cared. (The patch also exports page_cache_readahead() to GPL modules) Cc: "Stephen C. Tweedie" <sct@redhat.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
| * [PATCH] readahead: fix initial window size calculationSteven Pratt2006-03-221-3/+3
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | The current current get_init_ra_size is not optimal across different IO sizes and max_readahead values. Here is a quick summary of sizes computed under current design and under the attached patch. All of these assume 1st IO at offset 0, or 1st detected sequential IO. 32k max, 4k request old new ----------------- 8k 8k 16k 16k 32k 32k 128k max, 4k request old new ----------------- 32k 16k 64k 32k 128k 64k 128k 128k 128k max, 32k request old new ----------------- 32k 64k <----- 64k 128k 128k 128k 512k max, 4k request old new ----------------- 4k 32k <---- 16k 64k 64k 128k 128k 256k 512k 512k Cc: Oleg Nesterov <oleg@tv-sign.ru> Cc: Steven Pratt <slpratt@austin.ibm.com> Cc: Ram Pai <linuxram@us.ibm.com> Cc: Trond Myklebust <trond.myklebust@fys.uio.no> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
| * [PATCH] readahead: ->prev_page can overrun the ahead windowOleg Nesterov2006-03-221-6/+20
| | | | | | | | | | | | | | | | | | | | | | | | | | If get_next_ra_size() does not grow fast enough, ->prev_page can overrun the ahead window. This means the caller will read the pages from ->ahead_start + ->ahead_size to ->prev_page synchronously. Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru> Cc: Steven Pratt <slpratt@austin.ibm.com> Cc: Ram Pai <linuxram@us.ibm.com> Cc: Trond Myklebust <trond.myklebust@fys.uio.no> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
* | [GFS2] Export file_ra_state_initSteven Whitehouse2006-01-301-0/+1
|/ | | | | | | | Export file_ra_state_init so that its possible to use the already exported functions which require a struct ra_state as an argument from a module. Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>
* [PATCH] add AOP_TRUNCATED_PAGE, prepend AOP_ to WRITEPAGE_ACTIVATEZach Brown2006-01-031-6/+9
| | | | | | | | | | | | | | | readpage(), prepare_write(), and commit_write() callers are updated to understand the special return code AOP_TRUNCATED_PAGE in the style of writepage() and WRITEPAGE_ACTIVATE. AOP_TRUNCATED_PAGE tells the caller that the callee has unlocked the page and that the operation should be tried again with a new page. OCFS2 uses this to detect and work around a lock inversion in its aop methods. There should be no change in behaviour for methods that don't return AOP_TRUNCATED_PAGE. WRITEPAGE_ACTIVATE is also prepended with AOP_ for consistency and they are made enums so that kerneldoc can be used to document their semantics. Signed-off-by: Zach Brown <zach.brown@oracle.com>
* [PATCH] readahead commentaryAndrew Morton2005-11-071-9/+22
| | | | | | | | | | Add a few comments surrounding the generic readahead API. Also convert some ulongs into pgoff_t: the identifier for PAGE_CACHE_SIZE offsets into pagecache. Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
* [PATCH] readahead: reset cache_hit earlierSteven Pratt2005-09-071-0/+1
| | | | | | | | | We don't reset the cache hit count until after readahead does a successful readahead. This seems to leave a corner case open where we miss in cache, but don't restart the readhead right away. Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
* Linux-2.6.12-rc2v2.6.12-rc2Linus Torvalds2005-04-161-0/+557
Initial git repository build. I'm not bothering with the full history, even though we have it. We can create a separate "historical" git archive of that later if we want to, and in the meantime it's about 3.2GB when imported into git - space that would just make the early git days unnecessarily complicated, when we don't have a lot of good infrastructure for it. Let it rip!
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