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Date: Mon, 01 Jun 2015 17:00:56 +0800
From: Bob Liu <bob.liu@...cle.com>
To: Roger Pau Monné <roger.pau@...rix.com>
CC: xen-devel@...ts.xen.org, 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
On 06/01/2015 04:36 PM, Roger Pau Monné wrote:
> 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?
>
I think it's unnecessary to send an new iteration if there isn't any new comments
about multi-page ring series.
This patch is meaningful only after multi-page ring series, else there is no
difference(no memory can be saved).
So I think it's fine for this patch coming after multi-page ring series.
>> 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;
>
Sorry, I can't remember why I made the mistake here.
Will be fixed.
Thanks,
-Bob
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