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authorLars Ellenberg <lars.ellenberg@linbit.com>2018-12-20 17:23:42 +0100
committerJens Axboe <axboe@kernel.dk>2018-12-20 09:51:31 -0700
commitf31e583aa2c20892aca3add26957dee6ab80a534 (patch)
treecd57652fc773adee2e259c783a6abe30da88acfd /include/linux/drbd.h
parent9848b6ddd8c92305252f94592c5e278574e7a6ac (diff)
drbd: introduce P_ZEROES (REQ_OP_WRITE_ZEROES on the "wire")
And also re-enable partial-zero-out + discard aligned. With the introduction of REQ_OP_WRITE_ZEROES, we started to use that for both WRITE_ZEROES and DISCARDS, hoping that WRITE_ZEROES would "do what we want", UNMAP if possible, zero-out the rest. The example scenario is some LVM "thin" backend. While an un-allocated block on dm-thin reads as zeroes, on a dm-thin with "skip_block_zeroing=true", after a partial block write allocated that block, that same block may well map "undefined old garbage" from the backends on LBAs that have not yet been written to. If we cannot distinguish between zero-out and discard on the receiving side, to avoid "undefined old garbage" to pop up randomly at later times on supposedly zero-initialized blocks, we'd need to map all discards to zero-out on the receiving side. But that would potentially do a full alloc on thinly provisioned backends, even when the expectation was to unmap/trim/discard/de-allocate. We need to distinguish on the protocol level, whether we need to guarantee zeroes (and thus use zero-out, potentially doing the mentioned full-alloc), or if we want to put the emphasis on discard, and only do a "best effort zeroing" (by "discarding" blocks aligned to discard-granularity, and zeroing only potential unaligned head and tail clippings to at least *try* to avoid "false positives" in an online-verify later), hoping that someone set skip_block_zeroing=false. For some discussion regarding this on dm-devel, see also https://www.mail-archive.com/dm-devel%40redhat.com/msg07965.html https://www.redhat.com/archives/dm-devel/2018-January/msg00271.html For backward compatibility, P_TRIM means zero-out, unless the DRBD_FF_WZEROES feature flag is agreed upon during handshake. To have upper layers even try to submit WRITE ZEROES requests, we need to announce "efficient zeroout" independently. We need to fixup max_write_zeroes_sectors after blk_queue_stack_limits(): if we can handle "zeroes" efficiently on the protocol, we want to do that, even if our backend does not announce max_write_zeroes_sectors itself. Signed-off-by: Lars Ellenberg <lars.ellenberg@linbit.com> Signed-off-by: Jens Axboe <axboe@kernel.dk>
Diffstat (limited to 'include/linux/drbd.h')
-rw-r--r--include/linux/drbd.h2
1 files changed, 1 insertions, 1 deletions
diff --git a/include/linux/drbd.h b/include/linux/drbd.h
index 2d0259327721..a19d98367f08 100644
--- a/include/linux/drbd.h
+++ b/include/linux/drbd.h
@@ -51,7 +51,7 @@
#endif
extern const char *drbd_buildtag(void);
-#define REL_VERSION "8.4.10"
+#define REL_VERSION "8.4.11"
#define API_VERSION 1
#define PRO_VERSION_MIN 86
#define PRO_VERSION_MAX 101