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Date: Mon, 1 Jun 2015 10:36:20 +0200
From: Roger Pau Monné <roger.pau@...rix.com>
To: Bob Liu <bob.liu@...cle.com>, <xen-devel@...ts.xen.org>
CC: <david.vrabel@...rix.com>, <justing@...ctralogic.com>,
<konrad.wilk@...cle.com>, <paul.durrant@...rix.com>,
<julien.grall@...rix.com>, <boris.ostrovsky@...cle.com>,
<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] drivers: xen-blkback: delay pending_req allocation to
connect_ring
El 26/05/15 a les 2.06, Bob Liu ha escrit:
> In connect_ring, we can know exactly how many pages are used for the shared
> ring and also whether feature-persistent is enabled, delay pending_req
> allocation here so that we won't waste too much memory.
I would very much prefer for this to be a pre-patch for your multipage
ring series. Do you think you can include it in the next iteration?
> Signed-off-by: Bob Liu <bob.liu@...cle.com>
> ---
> drivers/block/xen-blkback/common.h | 3 +-
> drivers/block/xen-blkback/xenbus.c | 95 ++++++++++++++++++++------------------
> 2 files changed, 51 insertions(+), 47 deletions(-)
>
> diff --git a/drivers/block/xen-blkback/common.h b/drivers/block/xen-blkback/common.h
> index 919a1ab..e1d605d 100644
> --- a/drivers/block/xen-blkback/common.h
> +++ b/drivers/block/xen-blkback/common.h
> @@ -249,7 +249,7 @@ struct backend_info;
> #define PERSISTENT_GNT_WAS_ACTIVE 1
>
> /* Number of requests that we can fit in a ring */
> -#define XEN_MAX_BLKIF_REQS (32 * XENBUS_MAX_RING_PAGES)
> +#define XEN_BLKIF_REQS 32
This should be XEN_BLKIF_REQS_PER_PAGE (or a similar name of your choice
that reflects that those are the number of requests per ring page).
>
> struct persistent_gnt {
> struct page *page;
> @@ -321,6 +321,7 @@ struct xen_blkif {
> struct work_struct free_work;
> /* Thread shutdown wait queue. */
> wait_queue_head_t shutdown_wq;
> + unsigned int nr_ring_pages;
> };
>
> struct seg_buf {
> diff --git a/drivers/block/xen-blkback/xenbus.c b/drivers/block/xen-blkback/xenbus.c
> index bc33888..48336a3 100644
> --- a/drivers/block/xen-blkback/xenbus.c
> +++ b/drivers/block/xen-blkback/xenbus.c
> @@ -125,8 +125,6 @@ static void xen_update_blkif_status(struct xen_blkif *blkif)
> static struct xen_blkif *xen_blkif_alloc(domid_t domid)
> {
> struct xen_blkif *blkif;
> - struct pending_req *req, *n;
> - int i, j;
>
> BUILD_BUG_ON(MAX_INDIRECT_PAGES > BLKIF_MAX_INDIRECT_PAGES_PER_REQUEST);
>
> @@ -153,50 +151,11 @@ static struct xen_blkif *xen_blkif_alloc(domid_t domid)
> INIT_LIST_HEAD(&blkif->pending_free);
> INIT_WORK(&blkif->free_work, xen_blkif_deferred_free);
>
> - for (i = 0; i < XEN_MAX_BLKIF_REQS; i++) {
> - req = kzalloc(sizeof(*req), GFP_KERNEL);
> - if (!req)
> - goto fail;
> - list_add_tail(&req->free_list,
> - &blkif->pending_free);
> - for (j = 0; j < MAX_INDIRECT_SEGMENTS; j++) {
> - req->segments[j] = kzalloc(sizeof(*req->segments[0]),
> - GFP_KERNEL);
> - if (!req->segments[j])
> - goto fail;
> - }
> - for (j = 0; j < MAX_INDIRECT_PAGES; j++) {
> - req->indirect_pages[j] = kzalloc(sizeof(*req->indirect_pages[0]),
> - GFP_KERNEL);
> - if (!req->indirect_pages[j])
> - goto fail;
> - }
> - }
> spin_lock_init(&blkif->pending_free_lock);
> init_waitqueue_head(&blkif->pending_free_wq);
> init_waitqueue_head(&blkif->shutdown_wq);
>
> return blkif;
> -
> -fail:
> - list_for_each_entry_safe(req, n, &blkif->pending_free, free_list) {
> - list_del(&req->free_list);
> - for (j = 0; j < MAX_INDIRECT_SEGMENTS; j++) {
> - if (!req->segments[j])
> - break;
> - kfree(req->segments[j]);
> - }
> - for (j = 0; j < MAX_INDIRECT_PAGES; j++) {
> - if (!req->indirect_pages[j])
> - break;
> - kfree(req->indirect_pages[j]);
> - }
> - kfree(req);
> - }
> -
> - kmem_cache_free(xen_blkif_cachep, blkif);
> -
> - return ERR_PTR(-ENOMEM);
> }
>
> static int xen_blkif_map(struct xen_blkif *blkif, grant_ref_t *gref,
> @@ -313,7 +272,7 @@ static void xen_blkif_free(struct xen_blkif *blkif)
> i++;
> }
>
> - WARN_ON(i != XEN_MAX_BLKIF_REQS);
> + WARN_ON(i != XEN_BLKIF_REQS * blkif->nr_ring_pages);
>
> kmem_cache_free(xen_blkif_cachep, blkif);
> }
> @@ -868,9 +827,10 @@ static int connect_ring(struct backend_info *be)
> struct xenbus_device *dev = be->dev;
> unsigned int ring_ref[XENBUS_MAX_RING_PAGES];
> unsigned int evtchn, nr_grefs, ring_page_order;
> - unsigned int pers_grants;
> + unsigned int pers_grants, i, j;
> + struct pending_req *req, *n;
> char protocol[64] = "";
> - int err;
> + int err, nr_indiret_pages, nr_segs;
^ nr_indirect_pages (notice the missing 'c').
>
> pr_debug("%s %s\n", __func__, dev->otherend);
>
> @@ -899,8 +859,6 @@ static int connect_ring(struct backend_info *be)
> pr_info("%s:using single page: ring-ref %d\n", dev->otherend,
> ring_ref[0]);
> } else {
> - unsigned int i;
> -
> if (ring_page_order > xen_blkif_max_ring_order) {
> err = -EINVAL;
> xenbus_dev_fatal(dev, err, "%s/request %d ring page order exceed max:%d",
> @@ -949,11 +907,39 @@ static int connect_ring(struct backend_info *be)
>
> be->blkif->vbd.feature_gnt_persistent = pers_grants;
> be->blkif->vbd.overflow_max_grants = 0;
> + be->blkif->nr_ring_pages = nr_grefs;
>
> pr_info("ring-pages:%d, event-channel %d, protocol %d (%s) %s\n",
> nr_grefs, evtchn, be->blkif->blk_protocol, protocol,
> pers_grants ? "persistent grants" : "");
>
> + if (!pers_grants) {
> + nr_indiret_pages = 0;
> + nr_segs = BLKIF_MAX_SEGMENTS_PER_REQUEST;
> + } else {
> + nr_indiret_pages = MAX_INDIRECT_PAGES;
> + nr_segs = MAX_INDIRECT_SEGMENTS;
> + }
This is not right, persistent grants and indirect descriptors are
features that can be used independently, so AFAICT this has to be:
nr_indiret_pages = MAX_INDIRECT_PAGES;
nr_segs = MAX_INDIRECT_SEGMENTS;
Roger.
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