Consecutive zone device pages should not be merged into the same sgl
or bvec segment with other types of pages or if they belong to different
pgmaps. Otherwise getting the pgmap of a given segment is not possible
without scanning the entire segment. This helper returns true either if
both pages are not zone device pages or both pages are zone device
pages with the same pgmap.
Factor out the check for page mergability into a pages_are_mergable()
helper and add a check with zone_device_pages_are_mergeable().
Signed-off-by: Logan Gunthorpe <[email protected]>
---
lib/scatterlist.c | 25 +++++++++++++++----------
1 file changed, 15 insertions(+), 10 deletions(-)
diff --git a/lib/scatterlist.c b/lib/scatterlist.c
index c8c3d675845c..a0ad2a7959b5 100644
--- a/lib/scatterlist.c
+++ b/lib/scatterlist.c
@@ -410,6 +410,15 @@ static struct scatterlist *get_next_sg(struct sg_append_table *table,
return new_sg;
}
+static bool pages_are_mergeable(struct page *a, struct page *b)
+{
+ if (page_to_pfn(a) != page_to_pfn(b) + 1)
+ return false;
+ if (!zone_device_pages_have_same_pgmap(a, b))
+ return false;
+ return true;
+}
+
/**
* sg_alloc_append_table_from_pages - Allocate and initialize an append sg
* table from an array of pages
@@ -447,6 +456,7 @@ int sg_alloc_append_table_from_pages(struct sg_append_table *sgt_append,
unsigned int chunks, cur_page, seg_len, i, prv_len = 0;
unsigned int added_nents = 0;
struct scatterlist *s = sgt_append->prv;
+ struct page *last_pg;
/*
* The algorithm below requires max_segment to be aligned to PAGE_SIZE
@@ -460,21 +470,17 @@ int sg_alloc_append_table_from_pages(struct sg_append_table *sgt_append,
return -EOPNOTSUPP;
if (sgt_append->prv) {
- unsigned long paddr =
- (page_to_pfn(sg_page(sgt_append->prv)) * PAGE_SIZE +
- sgt_append->prv->offset + sgt_append->prv->length) /
- PAGE_SIZE;
-
if (WARN_ON(offset))
return -EINVAL;
/* Merge contiguous pages into the last SG */
prv_len = sgt_append->prv->length;
- while (n_pages && page_to_pfn(pages[0]) == paddr) {
+ last_pg = sg_page(sgt_append->prv);
+ while (n_pages && pages_are_mergeable(last_pg, pages[0])) {
if (sgt_append->prv->length + PAGE_SIZE > max_segment)
break;
sgt_append->prv->length += PAGE_SIZE;
- paddr++;
+ last_pg = pages[0];
pages++;
n_pages--;
}
@@ -488,7 +494,7 @@ int sg_alloc_append_table_from_pages(struct sg_append_table *sgt_append,
for (i = 1; i < n_pages; i++) {
seg_len += PAGE_SIZE;
if (seg_len >= max_segment ||
- page_to_pfn(pages[i]) != page_to_pfn(pages[i - 1]) + 1) {
+ !pages_are_mergeable(pages[i], pages[i - 1])) {
chunks++;
seg_len = 0;
}
@@ -504,8 +510,7 @@ int sg_alloc_append_table_from_pages(struct sg_append_table *sgt_append,
for (j = cur_page + 1; j < n_pages; j++) {
seg_len += PAGE_SIZE;
if (seg_len >= max_segment ||
- page_to_pfn(pages[j]) !=
- page_to_pfn(pages[j - 1]) + 1)
+ !pages_are_mergeable(pages[j], pages[j - 1]))
break;
}
--
2.30.2
Looks good:
Reviewed-by: Christoph Hellwig <[email protected]>
On 8/25/22 08:24, Logan Gunthorpe wrote:
> Consecutive zone device pages should not be merged into the same sgl
> or bvec segment with other types of pages or if they belong to different
> pgmaps. Otherwise getting the pgmap of a given segment is not possible
> without scanning the entire segment. This helper returns true either if
> both pages are not zone device pages or both pages are zone device
> pages with the same pgmap.
>
> Factor out the check for page mergability into a pages_are_mergable()
> helper and add a check with zone_device_pages_are_mergeable().
>
> Signed-off-by: Logan Gunthorpe <[email protected]>
> ---
> lib/scatterlist.c | 25 +++++++++++++++----------
> 1 file changed, 15 insertions(+), 10 deletions(-)
>
> diff --git a/lib/scatterlist.c b/lib/scatterlist.c
> index c8c3d675845c..a0ad2a7959b5 100644
> --- a/lib/scatterlist.c
> +++ b/lib/scatterlist.c
> @@ -410,6 +410,15 @@ static struct scatterlist *get_next_sg(struct sg_append_table *table,
> return new_sg;
> }
>
> +static bool pages_are_mergeable(struct page *a, struct page *b)
> +{
> + if (page_to_pfn(a) != page_to_pfn(b) + 1)
Instead of "a" and "b", how about naming these args something like
"page" and "prev_page", in order to avoid giving the impression that
comparing a and b is the same as comparing b and a?
In other words, previously, as an unrolled function, the code made
sense:
page_to_pfn(pages[j]) != page_to_pfn(pages[j - 1]) + 1)
But now, the understanding that this *must* be called with a page and
its previous page has gotten lost during refactoring, and we are left
with a check that is, on its own, not understandable.
Otherwise, the diffs look good. With some sort of naming change to
the args there, please feel free to add:
Reviewed-by: John Hubbard <[email protected]>
thanks,
--
John Hubbard
NVIDIA
> + return false;
> + if (!zone_device_pages_have_same_pgmap(a, b))
> + return false;
> + return true;
> +}
> +
> /**
> * sg_alloc_append_table_from_pages - Allocate and initialize an append sg
> * table from an array of pages
> @@ -447,6 +456,7 @@ int sg_alloc_append_table_from_pages(struct sg_append_table *sgt_append,
> unsigned int chunks, cur_page, seg_len, i, prv_len = 0;
> unsigned int added_nents = 0;
> struct scatterlist *s = sgt_append->prv;
> + struct page *last_pg;
>
> /*
> * The algorithm below requires max_segment to be aligned to PAGE_SIZE
> @@ -460,21 +470,17 @@ int sg_alloc_append_table_from_pages(struct sg_append_table *sgt_append,
> return -EOPNOTSUPP;
>
> if (sgt_append->prv) {
> - unsigned long paddr =
> - (page_to_pfn(sg_page(sgt_append->prv)) * PAGE_SIZE +
> - sgt_append->prv->offset + sgt_append->prv->length) /
> - PAGE_SIZE;
> -
> if (WARN_ON(offset))
> return -EINVAL;
>
> /* Merge contiguous pages into the last SG */
> prv_len = sgt_append->prv->length;
> - while (n_pages && page_to_pfn(pages[0]) == paddr) {
> + last_pg = sg_page(sgt_append->prv);
> + while (n_pages && pages_are_mergeable(last_pg, pages[0])) {
> if (sgt_append->prv->length + PAGE_SIZE > max_segment)
> break;
> sgt_append->prv->length += PAGE_SIZE;
> - paddr++;
> + last_pg = pages[0];
> pages++;
> n_pages--;
> }
> @@ -488,7 +494,7 @@ int sg_alloc_append_table_from_pages(struct sg_append_table *sgt_append,
> for (i = 1; i < n_pages; i++) {
> seg_len += PAGE_SIZE;
> if (seg_len >= max_segment ||
> - page_to_pfn(pages[i]) != page_to_pfn(pages[i - 1]) + 1) {
> + !pages_are_mergeable(pages[i], pages[i - 1])) {
> chunks++;
> seg_len = 0;
> }
> @@ -504,8 +510,7 @@ int sg_alloc_append_table_from_pages(struct sg_append_table *sgt_append,
> for (j = cur_page + 1; j < n_pages; j++) {
> seg_len += PAGE_SIZE;
> if (seg_len >= max_segment ||
> - page_to_pfn(pages[j]) !=
> - page_to_pfn(pages[j - 1]) + 1)
> + !pages_are_mergeable(pages[j], pages[j - 1]))
> break;
> }
>