| Message ID | 20170126115819.58875-6-kirill.shutemov@linux.intel.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Thu, Jan 26, 2017 at 02:57:47PM +0300, Kirill A. Shutemov wrote: > @@ -2146,6 +2146,23 @@ int split_huge_page_to_list(struct page *page, struct list_head *list) > goto out; > } > > + /* Try to free buffers before attempt split */ > + if (!PageSwapBacked(head) && PagePrivate(page)) { > + /* > + * We cannot trigger writeback from here due possible > + * recursion if triggered from vmscan, only wait. > + * > + * Caller can trigger writeback it on its own, if safe. > + */ It took me a few reads to get this. May I suggest: /* * Cannot split a page with buffers. If the caller has * already started writeback, we can wait for it to finish, * but we cannot start writeback if we were called from vmscan */ > + if (!PageSwapBacked(head) && PagePrivate(page)) { Also, it looks weird to test PageSwapBacked of *head* and PagePrivate of *page*. I think it's correct, but it still looks weird. Reviewed-by: Matthew Wilcox <mawilcox@microsoft.com>
On Thu, Feb 09, 2017 at 12:14:16PM -0800, Matthew Wilcox wrote: > On Thu, Jan 26, 2017 at 02:57:47PM +0300, Kirill A. Shutemov wrote: > > @@ -2146,6 +2146,23 @@ int split_huge_page_to_list(struct page *page, struct list_head *list) > > goto out; > > } > > > > + /* Try to free buffers before attempt split */ > > + if (!PageSwapBacked(head) && PagePrivate(page)) { > > + /* > > + * We cannot trigger writeback from here due possible > > + * recursion if triggered from vmscan, only wait. > > + * > > + * Caller can trigger writeback it on its own, if safe. > > + */ > > It took me a few reads to get this. May I suggest: > > /* > * Cannot split a page with buffers. If the caller has > * already started writeback, we can wait for it to finish, > * but we cannot start writeback if we were called from vmscan > */ Yeah, that's better. > > + if (!PageSwapBacked(head) && PagePrivate(page)) { > > Also, it looks weird to test PageSwapBacked of *head* and PagePrivate > of *page*. I think it's correct, but it still looks weird. I'll change this. > Reviewed-by: Matthew Wilcox <mawilcox@microsoft.com> Thanks!
diff --git a/include/linux/buffer_head.h b/include/linux/buffer_head.h index d67ab83823ad..fd4134ce9c54 100644 --- a/include/linux/buffer_head.h +++ b/include/linux/buffer_head.h @@ -400,6 +400,7 @@ extern int __set_page_dirty_buffers(struct page *page); #else /* CONFIG_BLOCK */ static inline void buffer_init(void) {} +static inline int page_has_buffers(struct page *page) { return 0; } static inline int try_to_free_buffers(struct page *page) { return 1; } static inline int inode_has_buffers(struct inode *inode) { return 0; } static inline void invalidate_inode_buffers(struct inode *inode) {} diff --git a/mm/huge_memory.c b/mm/huge_memory.c index 89819fe4debc..55aee62e8444 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -30,6 +30,7 @@ #include <linux/userfaultfd_k.h> #include <linux/page_idle.h> #include <linux/shmem_fs.h> +#include <linux/buffer_head.h> #include <asm/tlb.h> #include <asm/pgalloc.h> @@ -2117,7 +2118,6 @@ int split_huge_page_to_list(struct page *page, struct list_head *list) VM_BUG_ON_PAGE(is_huge_zero_page(page), page); VM_BUG_ON_PAGE(!PageLocked(page), page); - VM_BUG_ON_PAGE(!PageSwapBacked(page), page); VM_BUG_ON_PAGE(!PageCompound(page), page); if (PageAnon(head)) { @@ -2146,6 +2146,23 @@ int split_huge_page_to_list(struct page *page, struct list_head *list) goto out; } + /* Try to free buffers before attempt split */ + if (!PageSwapBacked(head) && PagePrivate(page)) { + /* + * We cannot trigger writeback from here due possible + * recursion if triggered from vmscan, only wait. + * + * Caller can trigger writeback it on its own, if safe. + */ + wait_on_page_writeback(head); + + if (page_has_buffers(head) && !try_to_release_page(head, + GFP_KERNEL)) { + ret = -EBUSY; + goto out; + } + } + /* Addidional pin from radix tree */ extra_pins = 1; anon_vma = NULL;
We want page to be isolated from the rest of the system before splitting it. We rely on page count to be 2 for file pages to make sure nobody uses the page: one pin to caller, one to radix-tree. Filesystems with backing storage can have page count increased if it has buffers. Let's try to free them, before attempt split. And remove one guarding VM_BUG_ON_PAGE(). Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> --- include/linux/buffer_head.h | 1 + mm/huge_memory.c | 19 ++++++++++++++++++- 2 files changed, 19 insertions(+), 1 deletion(-)