diff options
Diffstat (limited to 'module/os/linux')
| -rw-r--r-- | module/os/linux/zfs/abd_os.c | 14 |
1 files changed, 14 insertions, 0 deletions
diff --git a/module/os/linux/zfs/abd_os.c b/module/os/linux/zfs/abd_os.c index 3fe01c0b7..d3255dcbc 100644 --- a/module/os/linux/zfs/abd_os.c +++ b/module/os/linux/zfs/abd_os.c @@ -62,6 +62,7 @@ #include <linux/kmap_compat.h> #include <linux/mm_compat.h> #include <linux/scatterlist.h> +#include <linux/version.h> #endif #ifdef _KERNEL @@ -1061,6 +1062,7 @@ abd_iter_page(struct abd_iter *aiter) } ASSERT(page); +#if LINUX_VERSION_CODE >= KERNEL_VERSION(4, 5, 0) if (PageTail(page)) { /* * This page is part of a "compound page", which is a group of @@ -1082,11 +1084,23 @@ abd_iter_page(struct abd_iter *aiter) * To do this, we need to adjust the offset to be counted from * the head page. struct page for compound pages are stored * contiguously, so we can just adjust by a simple offset. + * + * Before kernel 4.5, compound page heads were refcounted + * separately, such that moving back to the head page would + * require us to take a reference to it and releasing it once + * we're completely finished with it. In practice, that means + * when our caller is done with the ABD, which we have no + * insight into from here. Rather than contort this API to + * track head page references on such ancient kernels, we just + * compile this block out and use the tail pages directly. This + * is slightly less efficient, but makes everything far + * simpler. */ struct page *head = compound_head(page); doff += ((page - head) * PAGESIZE); page = head; } +#endif /* final page and position within it */ aiter->iter_page = page; |