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Subject[RFC v2 33/43] PKRAM: atomically add and remove link pages
Date
Add and remove pkram_link pages from a pkram_obj atomically to prepare
for multithreading.

Signed-off-by: Anthony Yznaga <anthony.yznaga@oracle.com>
---
mm/pkram.c | 39 ++++++++++++++++++++++++---------------
1 file changed, 24 insertions(+), 15 deletions(-)

diff --git a/mm/pkram.c b/mm/pkram.c
index 08144c18d425..382ccf6f789f 100644
--- a/mm/pkram.c
+++ b/mm/pkram.c
@@ -535,33 +535,42 @@ static void pkram_truncate(void)
static void pkram_add_link(struct pkram_link *link, struct pkram_data_stream *pds)
{
__u64 link_pfn = page_to_pfn(virt_to_page(link));
+ __u64 *tail = pds->tail_link_pfnp;
+ __u64 tail_pfn;

- if (!*pds->head_link_pfnp) {
+ do {
+ tail_pfn = *tail;
+ } while (cmpxchg64(tail, tail_pfn, link_pfn) != tail_pfn);
+
+ if (!tail_pfn) {
*pds->head_link_pfnp = link_pfn;
- *pds->tail_link_pfnp = link_pfn;
} else {
- struct pkram_link *tail = pfn_to_kaddr(*pds->tail_link_pfnp);
+ struct pkram_link *prev_tail = pfn_to_kaddr(tail_pfn);

- tail->link_pfn = link_pfn;
- *pds->tail_link_pfnp = link_pfn;
+ prev_tail->link_pfn = link_pfn;
}
}

static struct pkram_link *pkram_remove_link(struct pkram_data_stream *pds)
{
- struct pkram_link *link;
+ __u64 *head = pds->head_link_pfnp;
+ __u64 head_pfn = *head;

- if (!*pds->head_link_pfnp)
- return NULL;
+ while (head_pfn) {
+ struct pkram_link *link = pfn_to_kaddr(head_pfn);

- link = pfn_to_kaddr(*pds->head_link_pfnp);
- *pds->head_link_pfnp = link->link_pfn;
- if (!*pds->head_link_pfnp)
- *pds->tail_link_pfnp = 0;
- else
- link->link_pfn = 0;
+ if (cmpxchg64(head, head_pfn, link->link_pfn) == head_pfn) {
+ if (!*head)
+ *pds->tail_link_pfnp = 0;
+ else
+ link->link_pfn = 0;
+ return link;
+ }

- return link;
+ head_pfn = *head;
+ }
+
+ return NULL;
}

static struct pkram_link *pkram_new_link(struct pkram_data_stream *pds, gfp_t gfp_mask)
--
1.8.3.1
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