> -----Original Message----- > From: Tim Smith [mailto:tim.sm...@citrix.com] > Sent: 02 November 2018 10:01 > To: xen-de...@lists.xenproject.org; qemu-devel@nongnu.org; qemu- > bl...@nongnu.org > Cc: Anthony Perard <anthony.per...@citrix.com>; Kevin Wolf > <kw...@redhat.com>; Paul Durrant <paul.durr...@citrix.com>; Stefano > Stabellini <sstabell...@kernel.org>; Max Reitz <mre...@redhat.com> > Subject: [PATCH 3/3] Avoid repeated memory allocation in xen_disk > > 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 <tim.sm...@citrix.com>
Reviewed-by: Paul Durrant <paul.durr...@citrix.com> > --- > hw/block/xen_disk.c | 11 ++++++----- > 1 file changed, 6 insertions(+), 5 deletions(-) > > diff --git a/hw/block/xen_disk.c b/hw/block/xen_disk.c > index b506e23868..faaeefba29 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 +136,11 @@ 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 +317,12 @@ 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 +394,10 @@ 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; > } > > @@ -990,6 +990,7 @@ 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); > } >