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2009-05-08bio: fix memcpy corruption in bio_copy_user_iov()FUJITA Tomonori
commit 69838727bcd819a8fd73a88447801221788b0c6d upstream. st driver uses blk_rq_map_user() in order to just build a request out of page frames. In this case, map_data->offset is a non zero value and iov[0].iov_base is NULL. We need to increase nr_pages for that. Cc: stable@kernel.org Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp> Signed-off-by: Jens Axboe <jens.axboe@oracle.com> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
2009-03-14block: fix memory leak in bio_clone()Li Zefan
If bio_integrity_clone() fails, bio_clone() returns NULL without freeing the newly allocated bio. Signed-off-by: Li Zefan <lizf@cn.fujitsu.com> Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2009-03-14block: Add gfp_mask parameter to bio_integrity_clone()un'ichi Nomura
Stricter gfp_mask might be required for clone allocation. For example, request-based dm may clone bio in interrupt context so it has to use GFP_ATOMIC. Signed-off-by: Kiyoshi Ueda <k-ueda@ct.jp.nec.com> Signed-off-by: Jun'ichi Nomura <j-nomura@ce.jp.nec.com> Acked-by: Martin K. Petersen <martin.petersen@oracle.com> Cc: Alasdair G Kergon <agk@redhat.com> Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2009-02-26block: fix bogus gcc warning for uninitialized var usageJens Axboe
Newer gcc throw this warning: fs/bio.c: In function ?bio_alloc_bioset?: fs/bio.c:305: warning: ?p? may be used uninitialized in this function since it cannot figure out that 'p' is only ever used if 'bs' is non-NULL. Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2009-02-18fs/bio: bio_alloc_bioset: pass right object ptr to mempool_freeSubhash Peddamallu
When freeing from bio pool use right ptr to account for bs->front_pad, instead of bio ptr, Signed-off-by: Subhash Peddamallu <subhash.peddamallu@gmail.com> Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2009-01-02[SCSI] block: make blk_rq_map_user take a NULL user-space buffer for WRITEFUJITA Tomonori
The commit 818827669d85b84241696ffef2de485db46b0b5e (block: make blk_rq_map_user take a NULL user-space buffer) extended blk_rq_map_user to accept a NULL user-space buffer with a READ command. It was necessary to convert sg to use the block layer mapping API. This patch extends blk_rq_map_user again for a WRITE command. It is necessary to convert st and osst drivers to use the block layer apping API. Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp> Acked-by: Jens Axboe <jens.axboe@oracle.com> Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>
2009-01-02[SCSI] block: fix the partial mappings with struct rq_map_dataFUJITA Tomonori
This fixes bio_copy_user_iov to properly handle the partial mappings with struct rq_map_data (which only sg uses for now but st and osst will shortly). It adds the offset member to struct rq_map_data and changes blk_rq_map_user to update it so that bio_copy_user_iov can add an appropriate page frame via bio_add_pc_page(). Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp> Acked-by: Jens Axboe <jens.axboe@oracle.com> Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>
2009-01-02[SCSI] block: fix bio_add_page misuse with rq_map_dataFUJITA Tomonori
This fixes bio_add_page misuse in bio_copy_user_iov with rq_map_data, which only sg uses now. rq_map_data carries page frames for bio_add_pc_page. bio_copy_user_iov uses bio_add_pc_page with a larger size than PAGE_SIZE. It's clearly wrong. Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp> Acked-by: Jens Axboe <jens.axboe@oracle.com> Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>
2008-12-29bio: get rid of bio_vec clearingJens Axboe
We don't need to clear the memory used for adding bio_vec entries, since nobody should be looking at members unitialized. Any valid use should be below bio->bi_vcnt, and that members up until that count must be valid since they were added through bio_add_page(). Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2008-12-29bio: add support for inlining a number of bio_vecs inside the bioJens Axboe
When we go and allocate a bio for IO, we actually do two allocations. One for the bio itself, and one for the bi_io_vec that holds the actual pages we are interested in. This feature inlines a definable amount of io vecs inside the bio itself, so we eliminate the bio_vec array allocation for IO's up to a certain size. It defaults to 4 vecs, which is typically 16k of IO. Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2008-12-29bio: allow individual slabs in the bio_setJens Axboe
Instead of having a global bio slab cache, add a reference to one in each bio_set that is created. This allows for personalized slabs in each bio_set, so that they can have bios of different sizes. This means we can personalize the bios we return. File systems may want to embed the bio inside another structure, to avoid allocation more items (and stuffing them in ->bi_private) after the get a bio. Or we may want to embed a number of bio_vecs directly at the end of a bio, to avoid doing two allocations to return a bio. This is now possible. Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2008-12-29bio: move the slab pointer inside the bio_setJens Axboe
In preparation for adding differently sized bios. Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2008-12-29bio: only mempool back the largest bio_vec slab cacheJens Axboe
We only very rarely need the mempool backing, so it makes sense to get rid of all but one of the mempool in a bio_set. So keep the largest bio_vec count mempool so we can always honor the largest allocation, and "upgrade" callers that fail. Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2008-11-26blktrace: port to tracepoints, updateIngo Molnar
Port to the new tracepoints API: split DEFINE_TRACE() and DECLARE_TRACE() sites. Spread them out to the usage sites, as suggested by Mathieu Desnoyers. Signed-off-by: Ingo Molnar <mingo@elte.hu> Acked-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
2008-11-26blktrace: port to tracepointsArnaldo Carvalho de Melo
This was a forward port of work done by Mathieu Desnoyers, I changed it to encode the 'what' parameter on the tracepoint name, so that one can register interest in specific events and not on classes of events to then check the 'what' parameter. Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com> Signed-off-by: Jens Axboe <jens.axboe@oracle.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-10-09block: mark bio_split_pool staticDenis ChengRq
Since all bio_split calls refer the same single bio_split_pool, the bio_split function can use bio_split_pool directly instead of the mempool_t parameter; then the mempool_t parameter can be removed from bio_split param list, and bio_split_pool is only referred in fs/bio.c file, can be marked static. Signed-off-by: Denis ChengRq <crquan@gmail.com> Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2008-10-09block: Find bio sector offset given idx and offsetMartin K. Petersen
Helper function to find the sector offset in a bio given bvec index and page offset. Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com> Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2008-10-09block: add bio_kmalloc()Jens Axboe
Not all callers need (or want!) the mempool backing guarentee, it essentially means that you can only use bio_alloc() for short allocations and not for preallocating some bio's at setup or init time. So add bio_kmalloc() which does the same thing as bio_alloc(), except it just uses kmalloc() as the backing instead of the bio mempools. Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2008-10-09block: make blk_rq_map_user take a NULL user-space bufferFUJITA Tomonori
This patch changes blk_rq_map_user to accept a NULL user-space buffer with a READ command if rq_map_data is not NULL. Thus a caller can pass page frames to lk_rq_map_user to just set up a request and bios with page frames propely. bio_uncopy_user (called via blk_rq_unmap_user) doesn't copy data to user space with such request. Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp> Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2008-10-09bio: convert bio_copy_kern to use bio_copy_userFUJITA Tomonori
bio_copy_kern and bio_copy_user are very similar. This converts bio_copy_kern to use bio_copy_user. Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp> Cc: Jens Axboe <jens.axboe@oracle.com> Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2008-10-09block: introduce struct rq_map_data to use reserved pagesFUJITA Tomonori
This patch introduces struct rq_map_data to enable bio_copy_use_iov() use reserved pages. Currently, bio_copy_user_iov allocates bounce pages but drivers/scsi/sg.c wants to allocate pages by itself and use them. struct rq_map_data can be used to pass allocated pages to bio_copy_user_iov. The current users of bio_copy_user_iov simply passes NULL (they don't want to use pre-allocated pages). Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp> Cc: Jens Axboe <jens.axboe@oracle.com> Cc: Douglas Gilbert <dougg@torque.net> Cc: Mike Christie <michaelc@cs.wisc.edu> Cc: James Bottomley <James.Bottomley@HansenPartnership.com> Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2008-10-09block: add gfp_mask argument to blk_rq_map_user and blk_rq_map_user_iovFUJITA Tomonori
Currently, blk_rq_map_user and blk_rq_map_user_iov always do GFP_KERNEL allocation. This adds gfp_mask argument to blk_rq_map_user and blk_rq_map_user_iov so sg can use it (sg always does GFP_ATOMIC allocation). Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp> Signed-off-by: Douglas Gilbert <dougg@torque.net> Cc: Mike Christie <michaelc@cs.wisc.edu> Cc: James Bottomley <James.Bottomley@HansenPartnership.com> Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2008-10-09block: add support for IO CPU affinityJens Axboe
This patch adds support for controlling the IO completion CPU of either all requests on a queue, or on a per-request basis. We export a sysfs variable (rq_affinity) which, if set, migrates completions of requests to the CPU that originally submitted it. A bio helper (bio_set_completion_cpu()) is also added, so that queuers can ask for completion on that specific CPU. In testing, this has been show to cut the system time by as much as 20-40% on synthetic workloads where CPU affinity is desired. This requires a little help from the architecture, so it'll only work as designed for archs that are using the new generic smp helper infrastructure. Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2008-10-09drop vmerge accountingMikulas Patocka
Remove hw_segments field from struct bio and struct request. Without virtual merge accounting they have no purpose. Signed-off-by: Mikulas Patocka <mpatocka@redhat.com> Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2008-10-09block: drop virtual merging accountingMikulas Patocka
Remove virtual merge accounting. Signed-off-by: Mikulas Patocka <mpatocka@redhat.com> Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2008-08-27bio: fix __bio_copy_iov() handling of bio->bv_lenFUJITA Tomonori
The commit c5dec1c3034f1ae3503efbf641ff3b0273b64797 introduced __bio_copy_iov() to add bounce support to blk_rq_map_user_iov. __bio_copy_iov() uses bio->bv_len to copy data for READ commands after the completion but it doesn't work with a request that partially completed. SCSI always completes a PC request as a whole but seems some don't. Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp> Cc: stable@kernel.org Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2008-08-27bio: fix bio_copy_kern() handling of bio->bv_lenFUJITA Tomonori
The commit 68154e90c9d1492d570671ae181d9a8f8530da55 introduced bio_copy_kern() to add bounce support to blk_rq_map_kern. bio_copy_kern() uses bio->bv_len to copy data for READ commands after the completion but it doesn't work with a request that partially completed. SCSI always completes a PC request as a whole but seems some don't. This patch fixes bio_copy_kern to handle the above case. As bio_copy_user does, bio_copy_kern uses struct bio_map_data to store struct bio_vec. Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp> Reported-by: Nix <nix@esperi.org.uk> Tested-by: Nix <nix@esperi.org.uk> Cc: stable@kernel.org Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2008-08-06bio: make use of bvec_nr_vecsDenis ChengRq
Since introduced in 7ba1ba12eee, it should be made use of. Signed-off-by: Denis ChengRq <crquan@gmail.com> Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2008-07-26dio: use get_user_pages_fastNick Piggin
Use get_user_pages_fast in the common/generic block and fs direct IO paths. Signed-off-by: Nick Piggin <npiggin@suse.de> Cc: Dave Kleikamp <shaggy@austin.ibm.com> Cc: Andy Whitcroft <apw@shadowen.org> Cc: Ingo Molnar <mingo@elte.hu> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Andi Kleen <andi@firstfloor.org> Cc: Dave Kleikamp <shaggy@austin.ibm.com> Cc: Badari Pulavarty <pbadari@us.ibm.com> Cc: Zach Brown <zach.brown@oracle.com> Cc: Jens Axboe <jens.axboe@oracle.com> Reviewed-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2008-07-03Add bvec_merge_data to handle stacked devices and ->merge_bvec()Alasdair G Kergon
When devices are stacked, one device's merge_bvec_fn may need to perform the mapping and then call one or more functions for its underlying devices. The following bio fields are used: bio->bi_sector bio->bi_bdev bio->bi_size bio->bi_rw using bio_data_dir() This patch creates a new struct bvec_merge_data holding a copy of those fields to avoid having to change them directly in the struct bio when going down the stack only to have to change them back again on the way back up. (And then when the bio gets mapped for real, the whole exercise gets repeated, but that's a problem for another day...) Signed-off-by: Alasdair G Kergon <agk@redhat.com> Cc: Neil Brown <neilb@suse.de> Cc: Milan Broz <mbroz@redhat.com> Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2008-07-03block: Block layer data integrity supportMartin K. Petersen
Some block devices support verifying the integrity of requests by way of checksums or other protection information that is submitted along with the I/O. This patch implements support for generating and verifying integrity metadata, as well as correctly merging, splitting and cloning bios and requests that have this extra information attached. See Documentation/block/data-integrity.txt for more information. Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com> Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2008-07-03block: Globalize bio_set and bio_vec_slabMartin K. Petersen
Move struct bio_set and biovec_slab definitions to bio.h so they can be used outside of bio.c. Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com> Reviewed-by: Jeff Moyer <jmoyer@redhat.com> Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2008-05-07docbook: fix bio missing parameterRandy Dunlap
Fix fs/bio.c kernel-doc parameter warning: Warning(linux-2.6.25-git14//fs/bio.c:972): No description found for parameter 'reading' Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com> Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2008-05-07block: use unitialized_var() in bio_alloc_bioset()Jens Axboe
Better than setting idx to some random value and it silences the same bogus gcc warning. Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2008-04-29block: add dma alignment and padding support to blk_rq_map_kernFUJITA Tomonori
This patch adds bio_copy_kern similar to bio_copy_user. blk_rq_map_kern uses bio_copy_kern instead of bio_map_kern if necessary. bio_copy_kern uses temporary pages and the bi_end_io callback frees these pages. bio_copy_kern saves the original kernel buffer at bio->bi_private it doesn't use something like struct bio_map_data to store the information about the caller. Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp> Cc: Tejun Heo <htejun@gmail.com> Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2008-04-21block: convert bio_copy_user to bio_copy_user_iovFUJITA Tomonori
This patch enables bio_copy_user to take struct sg_iovec (renamed bio_copy_user_iov). bio_copy_user uses bio_copy_user_iov internally as bio_map_user uses bio_map_user_iov. The major changes are: - adds sg_iovec array to struct bio_map_data - adds __bio_copy_iov that copy data between bio and sg_iovec. bio_copy_user_iov and bio_uncopy_user use it. Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp> Cc: Tejun Heo <htejun@gmail.com> Cc: Mike Christie <michaelc@cs.wisc.edu> Cc: James Bottomley <James.Bottomley@HansenPartnership.com> Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2008-03-17Revert "unexport bio_{,un}map_user"Jens Axboe
Outside users like asmlib uses the mapping functions. API wise, the export is definitely sane. It's a better idea to keep this export than to require external users to open-code this piece of code instead. Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2008-02-19fs/block_dev.c: remove #if 0'ed codeAdrian Bunk
Commit b2e895dbd80c420bfc0937c3729b4afe073b3848 #if 0'ed this code stating: <-- snip --> [PATCH] revert blockdev direct io back to 2.6.19 version Andrew Vasquez is reporting as-iosched oopses and a 65% throughput slowdown due to the recent special-casing of direct-io against blockdevs. We don't know why either of these things are occurring. The patch minimally reverts us back to the 2.6.19 code for a 2.6.20 release. <-- snip --> It has since been dead code, and unless someone wants to revive it now it's time to remove it. This patch also makes bio_release_pages() static again and removes the ki_bio_count member from struct kiocb, reverting changes that had been done for this dead code. Signed-off-by: Adrian Bunk <bunk@kernel.org> Signed-off-by: Jens Axboe <axboe@carl.home.kernel.dk>
2008-01-28__bio_clone: don't calculate hw/phys segment countsJens Axboe
If the users sets a new ->bi_bdev on the bio after __bio_clone() has returned it, the "segment counts valid" flag still remains even though it may be different with the new target. So don't calculate segment counts in __bio_clone(). Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2007-10-16bio: make freeing of ->bi_io_vec conditional in bio_free()Jens Axboe
The empty barrier patches do not carry data, so they have no iovec attached. Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2007-10-16bio: use memset() in bio_init()Jens Axboe
Use memset() to clear the bio, instead of doing each field manually. Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2007-10-10Drop 'size' argument from bio_endio and bi_end_ioNeilBrown
As bi_end_io is only called once when the reqeust is complete, the 'size' argument is now redundant. Remove it. Now there is no need for bio_endio to subtract the size completed from bi_size. So don't do that either. While we are at it, change bi_end_io to return void. Signed-off-by: Neil Brown <neilb@suse.de> Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2007-10-10Don't decrement bi_size in bio_endioNeilBrown
The only caller of bio_endio that does not pass the full bi_size is end_that_request_first. Also, no ->bi_end_io method is really interested in bi_size being decremented. So move the decrement and related code into ll_rw_blk and merge it with order_bio_endio to form req_bio_endio which does endio functionality specific to request completion. As some ->bi_end_io methods do check bi_size of 0, we set it thus for now, but that will go in the next patch. Signed-off-by: Neil Brown <neilb@suse.de> ### Diffstat output ./block/ll_rw_blk.c | 42 +++++++++++++++++++++++++++--------------- ./fs/bio.c | 23 +++++++++++------------ 2 files changed, 38 insertions(+), 27 deletions(-) diff .prev/block/ll_rw_blk.c ./block/ll_rw_blk.c Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2007-10-10Only call bi_end_io once for any bioNeilBrown
Currently bi_end_io can be called multiple times as sub-requests complete. However no ->bi_end_io function wants to know about that. So only call when the bio is complete. Signed-off-by: Neil Brown <neilb@suse.de> ### Diffstat output ./fs/bio.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff .prev/fs/bio.c ./fs/bio.c Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2007-07-24[BLOCK] Get rid of request_queue_t typedefJens Axboe
Some of the code has been gradually transitioned to using the proper struct request_queue, but there's lots left. So do a full sweet of the kernel and get rid of this typedef and replace its uses with the proper type. Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2007-07-20mm: Remove slab destructors from kmem_cache_create().Paul Mundt
Slab destructors were no longer supported after Christoph's c59def9f222d44bb7e2f0a559f2906191a0862d7 change. They've been BUGs for both slab and slub, and slob never supported them either. This rips out support for the dtor pointer from kmem_cache_create() completely and fixes up every single callsite in the kernel (there were about 224, not including the slab allocator definitions themselves, or the documentation references). Signed-off-by: Paul Mundt <lethal@linux-sh.org>
2007-07-10unexport bio_{,un}map_userAdrian Bunk
bio_{,un}map_user no longer have any modular users. Signed-off-by: Adrian Bunk <bunk@stusta.de> Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2007-05-07KMEM_CACHE(): simplify slab cache creationChristoph Lameter
This patch provides a new macro KMEM_CACHE(<struct>, <flags>) to simplify slab creation. KMEM_CACHE creates a slab with the name of the struct, with the size of the struct and with the alignment of the struct. Additional slab flags may be specified if necessary. Example struct test_slab { int a,b,c; struct list_head; } __cacheline_aligned_in_smp; test_slab_cache = KMEM_CACHE(test_slab, SLAB_PANIC) will create a new slab named "test_slab" of the size sizeof(struct test_slab) and aligned to the alignment of test slab. If it fails then we panic. 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>
2007-04-30[BLOCK] Don't pin lots of memory in mempoolsJens Axboe
Currently we scale the mempool sizes depending on memory installed in the machine, except for the bio pool itself which sits at a fixed 256 entry pre-allocation. There's really no point in "optimizing" this OOM path, we just need enough preallocated to make progress. A single unit is enough, lets scale it down to 2 just to be on the safe side. This patch saves ~150kb of pinned kernel memory on a 32-bit box. Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2006-12-13[PATCH] optimize o_direct on block devicesChen, Kenneth W
Implement block device specific .direct_IO method instead of going through generic direct_io_worker for block device. direct_io_worker() is fairly complex because it needs to handle O_DIRECT on file system, where it needs to perform block allocation, hole detection, extents file on write, and tons of other corner cases. The end result is that it takes tons of CPU time to submit an I/O. For block device, the block allocation is much simpler and a tight triple loop can be written to iterate each iovec and each page within the iovec in order to construct/prepare bio structure and then subsequently submit it to the block layer. This significantly speeds up O_D on block device. [akpm@osdl.org: small speedup] Signed-off-by: Ken Chen <kenneth.w.chen@intel.com> Cc: Christoph Hellwig <hch@lst.de> Cc: Zach Brown <zach.brown@oracle.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>