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Date: Mon, 17 Aug 2015 23:21:35 -0500
From: Bjorn Helgaas <bhelgaas@...gle.com>
To: Yinghai Lu <yinghai@...nel.org>
Cc: David Miller <davem@...emloft.net>,
Benjamin Herrenschmidt <benh@...nel.crashing.org>,
Wei Yang <weiyang@...ux.vnet.ibm.com>, TJ <linux@....tj>,
Yijing Wang <wangyijing@...wei.com>,
Andrew Morton <akpm@...ux-foundation.org>,
linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 33/51] resources: Make allocate_resource return just
fit resource
On Mon, Jul 27, 2015 at 04:29:51PM -0700, Yinghai Lu wrote:
> Find all suitable empty slots and pick one just fit, so we could save
> the big slot for needed ones later when we have several pcie switches
> and some bridges get assigned bios and we need to assign others in kernel.
By "just fit," do you mean "best fit"? "Best fit" is a well-known term, so
if that's what you mean, let's use it.
I couldn't quite parse the PCIe switch stuff here. How is that relevant to
this change?
> Signed-off-by: Yinghai Lu <yinghai@...nel.org>
> ---
> kernel/resource.c | 81 ++++++++++++++++++++++++++++++++++++++++++++++---------
> 1 file changed, 68 insertions(+), 13 deletions(-)
>
> diff --git a/kernel/resource.c b/kernel/resource.c
> index 67b58a5..697b8ca 100644
> --- a/kernel/resource.c
> +++ b/kernel/resource.c
> @@ -48,6 +48,7 @@ struct resource_constraint {
> resource_size_t (*alignf)(void *, const struct resource *,
> resource_size_t, resource_size_t);
> void *alignf_data;
> + bool fit;
> };
>
> static DEFINE_RWLOCK(resource_lock);
> @@ -554,12 +555,15 @@ static void resource_clip(struct resource *res, resource_size_t min,
> * alignment constraints
> */
> static int __find_resource(struct resource *root, struct resource *old,
> - struct resource *new,
> + struct resource *new, struct resource *avail,
> resource_size_t size,
> struct resource_constraint *constraint)
> {
> struct resource *this = root->child;
> - struct resource tmp = *new, avail, alloc;
> + struct resource tmp = *new, availx, alloc;
> +
> + if (!avail || avail == new)
> + avail = &availx;
>
> tmp.start = root->start;
> /*
> @@ -583,15 +587,16 @@ static int __find_resource(struct resource *root, struct resource *old,
> arch_remove_reservations(&tmp);
>
> /* Check for overflow after ALIGN() */
> - avail.start = ALIGN(tmp.start, constraint->align);
> - avail.end = tmp.end;
> - avail.flags = new->flags & ~IORESOURCE_UNSET;
> - if (avail.start >= tmp.start) {
> - alloc.flags = avail.flags;
> - alloc.start = constraint->alignf(constraint->alignf_data, &avail,
> + avail->start = ALIGN(tmp.start, constraint->align);
> + avail->end = tmp.end;
> + avail->flags = new->flags & ~IORESOURCE_UNSET;
> + if (avail->start >= tmp.start) {
> + alloc.flags = avail->flags;
> + alloc.start = constraint->alignf(
> + constraint->alignf_data, avail,
> size, constraint->align);
> alloc.end = alloc.start + size - 1;
> - if (resource_contains(&avail, &alloc)) {
> + if (resource_contains(avail, &alloc)) {
> new->start = alloc.start;
> new->end = alloc.end;
> return 0;
> @@ -608,6 +613,11 @@ next: if (!this || this->end == root->end)
> return -EBUSY;
> }
>
> +struct good_resource {
> + struct list_head list;
> + struct resource avail;
> + struct resource new;
> +};
> /*
> * Find empty slot in the resource tree given range and alignment.
> */
> @@ -615,7 +625,49 @@ static int find_resource(struct resource *root, struct resource *new,
> resource_size_t size,
> struct resource_constraint *constraint)
> {
> - return __find_resource(root, NULL, new, size, constraint);
> + int ret = -1;
> + LIST_HEAD(head);
> + struct good_resource *good, *tmp;
> + resource_size_t avail_size = (resource_size_t)-1ULL;
> +
> + if (!constraint->fit)
> + return __find_resource(root, NULL, new, NULL, size,
> + constraint);
> +
> + /* find all suitable ones and add to the list */
> + for (;;) {
> + good = kzalloc(sizeof(*good), GFP_KERNEL);
> + if (!good)
> + break;
> +
> + good->new.start = new->start;
> + good->new.end = new->end;
> + good->new.flags = new->flags;
> + ret = __find_resource(root, NULL, &good->new, &good->avail,
> + size, constraint);
> + if (ret || __request_resource(root, &good->avail)) {
> + ret = -EBUSY;
> + kfree(good);
> + break;
> + }
> +
> + list_add(&good->list, &head);
> + }
Allocating memory and building a list in a function that allocates space
seems like a little bit of a hack. I think we're holding resource_lock
anyway; can't we just find a candidate, reserve it, look for another one,
reserve it, release the larger one, and repeat?
> + /* pick up the smallest one and delete the list */
> + list_for_each_entry_safe(good, tmp, &head, list) {
> + if (resource_size(&good->avail) < avail_size) {
> + avail_size = resource_size(&good->avail);
> + new->start = good->new.start;
> + new->end = good->new.end;
> + ret = 0;
> + }
> + list_del(&good->list);
> + __release_resource(&good->avail);
> + kfree(good);
> + }
> +
> + return ret;
> }
>
> /**
> @@ -636,7 +688,8 @@ static int __reallocate_resource(struct resource *root, struct resource *old,
> struct resource new = *old;
> struct resource *conflict;
>
> - if ((err = __find_resource(root, old, &new, newsize, constraint)))
> + err = __find_resource(root, old, &new, NULL, newsize, constraint);
> + if (err)
> goto out;
>
> if (resource_contains(&new, old)) {
> @@ -675,6 +728,7 @@ out:
> * @align: alignment requested, in bytes
> * @alignf: alignment function, optional, called if not NULL
> * @alignf_data: arbitrary data to pass to the @alignf function
> + * @fit: only allocate fit range.
> *
> * Caller need to hold resource_lock if needed.
> */
> @@ -685,7 +739,7 @@ static int __allocate_resource(struct resource *root, struct resource *new,
> const struct resource *,
> resource_size_t,
> resource_size_t),
> - void *alignf_data)
> + void *alignf_data, bool fit)
> {
> int err;
> struct resource_constraint constraint;
> @@ -698,6 +752,7 @@ static int __allocate_resource(struct resource *root, struct resource *new,
> constraint.align = align;
> constraint.alignf = alignf;
> constraint.alignf_data = alignf_data;
> + constraint.fit = fit;
>
> if (new->parent) {
> /* resource is already allocated, try reallocating with
> @@ -738,7 +793,7 @@ int allocate_resource(struct resource *root, struct resource *new,
>
> write_lock(&resource_lock);
> ret = __allocate_resource(root, new, size, min, max, align,
> - alignf, alignf_data);
> + alignf, alignf_data, true);
> write_unlock(&resource_lock);
>
> return ret;
> --
> 1.8.4.5
>
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