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[Qemu-devel] [PATCH 3/3] Avoid repeated memory allocation in xen_disk
From: |
Tim Smith |
Subject: |
[Qemu-devel] [PATCH 3/3] Avoid repeated memory allocation in xen_disk |
Date: |
Fri, 7 Sep 2018 11:21:30 +0100 |
User-agent: |
StGit/0.17.1-dirty |
xen_disk currently allocates memory to hold the data for each ioreq
as that ioreq is used, and frees it afterwards. Because it requires
page-aligned blocks, this interacts poorly with non-page-aligned
allocations and balloons the heap.
Instead, allocate the maximum possible requirement, which is
BLKIF_MAX_SEGMENTS_PER_REQUEST pages (currently 11 pages) when
the ioreq is created, and keep that allocation until it is destroyed.
Since the ioreqs themselves are re-used via a free list, this
should actually improve memory usage.
Signed-off-by: Tim Smith <address@hidden>
---
hw/block/xen_disk.c | 10 +++++-----
1 file changed, 5 insertions(+), 5 deletions(-)
diff --git a/hw/block/xen_disk.c b/hw/block/xen_disk.c
index c11cd21d37..67f894bba5 100644
--- a/hw/block/xen_disk.c
+++ b/hw/block/xen_disk.c
@@ -112,7 +112,6 @@ static void ioreq_reset(struct ioreq *ioreq)
memset(&ioreq->req, 0, sizeof(ioreq->req));
ioreq->status = 0;
ioreq->start = 0;
- ioreq->buf = NULL;
ioreq->size = 0;
ioreq->presync = 0;
@@ -137,6 +136,10 @@ static struct ioreq *ioreq_start(struct XenBlkDev *blkdev)
/* allocate new struct */
ioreq = g_malloc0(sizeof(*ioreq));
ioreq->blkdev = blkdev;
+ /* We cannot need more pages per ioreq than this, and we do re-use
ioreqs,
+ * so allocate the memory once here, to be freed in blk_free() when the
+ * ioreq is freed. */
+ ioreq->buf = qemu_memalign(XC_PAGE_SIZE,
BLKIF_MAX_SEGMENTS_PER_REQUEST * XC_PAGE_SIZE);
blkdev->requests_total++;
qemu_iovec_init(&ioreq->v, 1);
} else {
@@ -313,14 +316,12 @@ static void qemu_aio_complete(void *opaque, int ret)
if (ret == 0) {
ioreq_grant_copy(ioreq);
}
- qemu_vfree(ioreq->buf);
break;
case BLKIF_OP_WRITE:
case BLKIF_OP_FLUSH_DISKCACHE:
if (!ioreq->req.nr_segments) {
break;
}
- qemu_vfree(ioreq->buf);
break;
default:
break;
@@ -392,12 +393,10 @@ static int ioreq_runio_qemu_aio(struct ioreq *ioreq)
{
struct XenBlkDev *blkdev = ioreq->blkdev;
- ioreq->buf = qemu_memalign(XC_PAGE_SIZE, ioreq->size);
if (ioreq->req.nr_segments &&
(ioreq->req.operation == BLKIF_OP_WRITE ||
ioreq->req.operation == BLKIF_OP_FLUSH_DISKCACHE) &&
ioreq_grant_copy(ioreq)) {
- qemu_vfree(ioreq->buf);
goto err;
}
@@ -989,6 +988,7 @@ static int blk_free(struct XenDevice *xendev)
ioreq = QLIST_FIRST(&blkdev->freelist);
QLIST_REMOVE(ioreq, list);
qemu_iovec_destroy(&ioreq->v);
+ qemu_vfree(ioreq->buf);
g_free(ioreq);
}