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authorMikulas Patocka <mpatocka@redhat.com>2011-08-02 12:32:04 +0100
committerAlasdair G Kergon <agk@redhat.com>2011-08-02 12:32:04 +0100
commita6e50b409d3f9e0833e69c3c9cca822e8fa4adbb (patch)
tree82ca807c21156437270e6a1ed255b18ccf8b3672 /include/linux/device-mapper.h
parentd5b9dd04bd74b774b8e8d93ced7a0d15ad403fa9 (diff)
dm snapshot: skip reading origin when overwriting complete chunk
If we write a full chunk in the snapshot, skip reading the origin device because the whole chunk will be overwritten anyway. This patch changes the snapshot write logic when a full chunk is written. In this case: 1. allocate the exception 2. dispatch the bio (but don't report the bio completion to device mapper) 3. write the exception record 4. report bio completed Callbacks must be done through the kcopyd thread, because callbacks must not race with each other. So we create two new functions: dm_kcopyd_prepare_callback: allocate a job structure and prepare the callback. (This function must not be called from interrupt context.) dm_kcopyd_do_callback: submit callback. (This function may be called from interrupt context.) Performance test (on snapshots with 4k chunk size): without the patch: non-direct-io sequential write (dd): 17.7MB/s direct-io sequential write (dd): 20.9MB/s non-direct-io random write (mkfs.ext2): 0.44s with the patch: non-direct-io sequential write (dd): 26.5MB/s direct-io sequential write (dd): 33.2MB/s non-direct-io random write (mkfs.ext2): 0.27s Signed-off-by: Mikulas Patocka <mpatocka@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
Diffstat (limited to 'include/linux/device-mapper.h')
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