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device: Skip read-modify-write if replacing whole block.

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This commit is contained in:
Alasdair G Kergon 2017-12-05 01:00:38 +00:00
parent e4805e4883
commit 7195df5aca
2 changed files with 14 additions and 9 deletions
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1
WHATS_NEW
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@ -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.

20
lib/device/dev-io.c
View File

@ -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;
@ -241,17 +242,18 @@ 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))
return _io(where, buffer, should_write, reason);
/* 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);
/* Allocate a bounce buffer with an extra block */
if (!(bounce_buf = bounce = dm_malloc((size_t) widened.size + block_size))) {
@ -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);
}