user/sven/linux.git/drivers/md/bcache/request.c, branch v5.5.11

bcache: add readahead cache policy options via sysfs interface

2020-02-11T12:37:06Z

commit 038ba8cc1bffc51250add4a9b9249d4331576d8f upstream. In year 2007 high performance SSD was still expensive, in order to save more space for real workload or meta data, the readahead I/Os for non-meta data was bypassed and not cached on SSD. In now days, SSD price drops a lot and people can find larger size SSD with more comfortable price. It is unncessary to alway bypass normal readahead I/Os to save SSD space for now. This patch adds options for readahead data cache policies via sysfs file /sys/block/bcache/readahead_cache_policy, the options are, - "all": cache all readahead data I/Os. - "meta-only": only cache meta data, and bypass other regular I/Os. If users want to make bcache continue to only cache readahead request for metadata and bypass regular data readahead, please set "meta-only" to this sysfs file. By default, bcache will back to cache all read- ahead requests now. Cc: stable@vger.kernel.org Signed-off-by: Coly Li Acked-by: Eric Wheeler Cc: Michael Lyle Signed-off-by: Jens Axboe Signed-off-by: Greg Kroah-Hartman

bcache: deleted code comments for dead code in bch_data_insert_keys()

2019-11-13T22:42:50Z

In request.c:bch_data_insert_keys(), there is code comment for a piece of dead code. This patch deletes the dead code and its code comment since they are useless in practice. Signed-off-by: Coly Li Signed-off-by: Jens Axboe

bcache: Clean up bch_get_congested()

2019-04-24T16:56:27Z

There are a few nits in this function. They could in theory all be separate patches, but that's probably taking small commits too far. 1) I added a brief comment saying what it does. 2) I like to declare pointer parameters "const" where possible for documentation reasons. 3) It uses bitmap_weight(&rand, BITS_PER_LONG) to compute the Hamming weight of a 32-bit random number (giving a random integer with mean 16 and variance 8). Passing by reference in a 64-bit variable is silly; just use hweight32(). 4) Its helper function fract_exp_two is unnecessarily tangled. Gcc can optimize the multiply by (1 << x) to a shift, but it can be written in a much more straightforward way at the cost of one more bit of internal precision. Some analysis reveals that this bit is always available. This shrinks the object code for fract_exp_two(x, 6) from 23 bytes: 0000000000000000 : 0: 89 f9 mov %edi,%ecx 2: c1 e9 06 shr $0x6,%ecx 5: b8 01 00 00 00 mov $0x1,%eax a: d3 e0 shl %cl,%eax c: 83 e7 3f and $0x3f,%edi f: d3 e7 shl %cl,%edi 11: c1 ef 06 shr $0x6,%edi 14: 01 f8 add %edi,%eax 16: c3 retq To 19: 0000000000000017 : 17: 89 f8 mov %edi,%eax 19: 83 e0 3f and $0x3f,%eax 1c: 83 c0 40 add $0x40,%eax 1f: 89 f9 mov %edi,%ecx 21: c1 e9 06 shr $0x6,%ecx 24: d3 e0 shl %cl,%eax 26: c1 e8 06 shr $0x6,%eax 29: c3 retq (Verified with 0 <= frac_bits <= 8, 0 <= x < 16< Signed-off-by: Coly Li Signed-off-by: Jens Axboe

bcache: fix crashes stopping bcache device before read miss done

2019-04-24T16:56:27Z

The bio from upper layer is considered completed when bio_complete() returns. In most scenarios bio_complete() is called in search_free(), but when read miss happens, the bio_compete() is called when backing device reading completed, while the struct search is still in use until cache inserting finished. If someone stops the bcache device just then, the device may be closed and released, but after cache inserting finished the struct search will access a freed struct cached_dev. This patch add the reference of bcache device before bio_complete() when read miss happens, and put it after the search is not used. Signed-off-by: Guoju Fang Signed-off-by: Coly Li Signed-off-by: Jens Axboe

bcache: use (REQ_META|REQ_PRIO) to indicate bio for metadata

2019-02-09T14:18:33Z

In 'commit 752f66a75aba ("bcache: use REQ_PRIO to indicate bio for metadata")' REQ_META is replaced by REQ_PRIO to indicate metadata bio. This assumption is not always correct, e.g. XFS uses REQ_META to mark metadata bio other than REQ_PRIO. This is why Nix noticed that bcache does not cache metadata for XFS after the above commit. Thanks to Dave Chinner, he explains the difference between REQ_META and REQ_PRIO from view of file system developer. Here I quote part of his explanation from mailing list, REQ_META is used for metadata. REQ_PRIO is used to communicate to the lower layers that the submitter considers this IO to be more important that non REQ_PRIO IO and so dispatch should be expedited. IOWs, if the filesystem considers metadata IO to be more important that user data IO, then it will use REQ_PRIO | REQ_META rather than just REQ_META. Then it seems bios with REQ_META or REQ_PRIO should both be cached for performance optimation, because they are all probably low I/O latency demand by upper layer (e.g. file system). So in this patch, when we want to decide whether to bypass the cache, REQ_META and REQ_PRIO are both checked. Then both metadata and high priority I/O requests will be handled properly. Reported-by: Nix Signed-off-by: Coly Li Reviewed-by: Andre Noll Tested-by: Nix Cc: stable@vger.kernel.org Cc: Dave Chinner Cc: Christoph Hellwig Signed-off-by: Jens Axboe

bcache: update comment for bch_data_insert

2018-12-13T15:15:54Z

commit 220bb38c21b8 ("bcache: Break up struct search") introduced changes to struct search and s->iop. bypass/bio are fields of struct data_insert_op now. Update the comment. Signed-off-by: Shenghui Wang Signed-off-by: Coly Li Signed-off-by: Jens Axboe

bcache: fix ioctl in flash device

2018-10-08T14:19:42Z

When doing ioctl in flash device, it will call ioctl_dev() in super.c, then we should not to get cached device since flash only device has no backend device. This patch just move the jugement dc->io_disable to cached_dev_ioctl() to make ioctl in flash device correctly. Fixes: 0f0709e6bfc3c ("bcache: stop bcache device when backing device is offline") Signed-off-by: Tang Junhui Cc: stable@vger.kernel.org Signed-off-by: Coly Li Signed-off-by: Jens Axboe

bcache: use REQ_PRIO to indicate bio for metadata

2018-10-08T14:19:40Z

In cached_dev_cache_miss() and check_should_bypass(), REQ_META is used to check whether a bio is for metadata request. REQ_META is used for blktrace, the correct REQ_ flag should be REQ_PRIO. This flag means the bio should be prior to other bio, and frequently be used to indicate metadata io in file system code. This patch replaces REQ_META with correct flag REQ_PRIO. CC Adam Manzanares because he explains to me what REQ_PRIO is for. Signed-off-by: Coly Li Cc: Adam Manzanares Signed-off-by: Jens Axboe

bcache: trace missed reading by cache_missed

2018-10-08T14:19:39Z

Missed reading IOs are identified by s->cache_missed, not the s->cache_miss, so in trace_bcache_read() using trace_bcache_read to identify whether the IO is missed or not. Signed-off-by: Tang Junhui Cc: stable@vger.kernel.org Signed-off-by: Coly Li Signed-off-by: Jens Axboe

bcache: do not check NULL pointer before calling kmem_cache_destroy

2018-08-11T21:46:42Z

kmem_cache_destroy() is safe for NULL pointer as input, the NULL pointer checking is unncessary. This patch just removes the NULL pointer checking to make code simpler. Signed-off-by: Coly Li Reviewed-by: Shenghui Wang Signed-off-by: Jens Axboe