From 1ff36b5d4d00a4e3633eb960bf2be562f5e47dbf Mon Sep 17 00:00:00 2001 From: Gerd Hoffmann Date: Fri, 30 Oct 2015 12:10:00 +0100 Subject: buffer: add buffer_shrink Signed-off-by: Gerd Hoffmann Reviewed-by: Peter Lieven Reviewed-by: Daniel P. Berrange Message-id: 1446203414-4013-6-git-send-email-kraxel@redhat.com --- include/qemu/buffer.h | 10 ++++++++++ util/buffer.c | 20 +++++++++++++++++++- 2 files changed, 29 insertions(+), 1 deletion(-) diff --git a/include/qemu/buffer.h b/include/qemu/buffer.h index 1358df1aac..0a69b3a972 100644 --- a/include/qemu/buffer.h +++ b/include/qemu/buffer.h @@ -51,6 +51,16 @@ struct Buffer { void buffer_init(Buffer *buffer, const char *name, ...) GCC_FMT_ATTR(2, 3); +/** + * buffer_shrink: + * @buffer: the buffer object + * + * Try to shrink the buffer. Checks current buffer capacity and size + * and reduces capacity in case only a fraction of the buffer is + * actually used. + */ +void buffer_shrink(Buffer *buffer); + /** * buffer_reserve: * @buffer: the buffer object diff --git a/util/buffer.c b/util/buffer.c index e8f798e620..234e33d5c1 100644 --- a/util/buffer.c +++ b/util/buffer.c @@ -20,7 +20,8 @@ #include "qemu/buffer.h" -#define BUFFER_MIN_INIT_SIZE 4096 +#define BUFFER_MIN_INIT_SIZE 4096 +#define BUFFER_MIN_SHRINK_SIZE 65536 void buffer_init(Buffer *buffer, const char *name, ...) { @@ -31,6 +32,23 @@ void buffer_init(Buffer *buffer, const char *name, ...) va_end(ap); } +void buffer_shrink(Buffer *buffer) +{ + /* + * Only shrink in case the used size is *much* smaller than the + * capacity, to avoid bumping up & down the buffers all the time. + * realloc() isn't exactly cheap ... + */ + if (buffer->offset < (buffer->capacity >> 3) && + buffer->capacity > BUFFER_MIN_SHRINK_SIZE) { + return; + } + + buffer->capacity = pow2ceil(buffer->offset); + buffer->capacity = MAX(buffer->capacity, BUFFER_MIN_SHRINK_SIZE); + buffer->buffer = g_realloc(buffer->buffer, buffer->capacity); +} + void buffer_reserve(Buffer *buffer, size_t len) { if ((buffer->capacity - buffer->offset) < len) { -- cgit v1.2.3