From 7195df5acace29e77add6aa2f3df9c684e44694a Mon Sep 17 00:00:00 2001 From: Alasdair G Kergon Date: Tue, 5 Dec 2017 01:00:38 +0000 Subject: [PATCH] device: Skip read-modify-write if replacing whole block. --- WHATS_NEW | 1 + lib/device/dev-io.c | 22 +++++++++++++--------- 2 files changed, 14 insertions(+), 9 deletions(-) diff --git a/WHATS_NEW b/WHATS_NEW index 541d76470..674e7f194 100644 --- a/WHATS_NEW +++ b/WHATS_NEW @@ -1,5 +1,6 @@ Version 2.02.177 - ==================================== + Skip read-modify-write when entire block is replaced. Categorise I/O with reason annotations in debug messages. Command will lock memory only when suspending volumes. Merge segments when pvmove is finished. diff --git a/lib/device/dev-io.c b/lib/device/dev-io.c index e108437e3..f77494f1a 100644 --- a/lib/device/dev-io.c +++ b/lib/device/dev-io.c @@ -231,6 +231,7 @@ static int _aligned_io(struct device_area *where, char *buffer, char *bounce, *bounce_buf; unsigned int physical_block_size = 0; unsigned int block_size = 0; + unsigned buffer_was_widened = 0; uintptr_t mask; struct device_area widened; int r = 0; @@ -241,18 +242,19 @@ static int _aligned_io(struct device_area *where, char *buffer, if (!block_size) block_size = lvm_getpagesize(); + mask = block_size - 1; _widen_region(block_size, where, &widened); - /* Do we need to use a bounce buffer? */ - mask = block_size - 1; - if (!memcmp(where, &widened, sizeof(widened)) && - !((uintptr_t) buffer & mask)) + /* Did we widen the buffer? When writing, this means means read-modify-write. */ + if (where->size != widened.size || where->start != widened.start) { + buffer_was_widened = 1; + log_debug_io("Widening request for %" PRIu64 " bytes at %" PRIu64 " to %" PRIu64 " bytes at %" PRIu64 " on %s (for %s)", + where->size, (uint64_t) where->start, widened.size, (uint64_t) widened.start, dev_name(where->dev), _reason_text(reason)); + } else if (!((uintptr_t) buffer & mask)) + /* Perform the I/O directly. */ return _io(where, buffer, should_write, reason); - log_debug_io("Widening request for %" PRIu64 " bytes at %" PRIu64 " to %" PRIu64 " bytes at %" PRIu64 " on %s (for %s)", - where->size, (uint64_t) where->start, widened.size, (uint64_t) widened.start, dev_name(where->dev), _reason_text(reason)); - /* Allocate a bounce buffer with an extra block */ if (!(bounce_buf = bounce = dm_malloc((size_t) widened.size + block_size))) { log_error("Bounce buffer malloc failed"); @@ -265,10 +267,12 @@ static int _aligned_io(struct device_area *where, char *buffer, if (((uintptr_t) bounce) & mask) bounce = (char *) ((((uintptr_t) bounce) + mask) & ~mask); - /* channel the io through the bounce buffer */ - if (!_io(&widened, bounce, 0, reason)) { + /* Do we need to read into the bounce buffer? */ + if ((!should_write || buffer_was_widened) && + !_io(&widened, bounce, 0, reason)) { if (!should_write) goto_out; + /* FIXME Handle errors properly! */ /* FIXME pre-extend the file */ memset(bounce, '\n', widened.size); }