[PATCH v8 02/22] Allow page fault handlers to perform the COW
From: Matthew Wilcox <hidden>
Date: 2014-07-22 19:47:50
Also in:
linux-fsdevel, lkml
Subsystem:
memory management, memory management - core, the rest · Maintainers:
Andrew Morton, David Hildenbrand, Linus Torvalds
Currently COW of an XIP file is done by first bringing in a read-only mapping, then retrying the fault and copying the page. It is much more efficient to tell the fault handler that a COW is being attempted (by passing in the pre-allocated page in the vm_fault structure), and allow the handler to perform the COW operation itself. Signed-off-by: Matthew Wilcox <redacted> Reviewed-by: Jan Kara <jack@suse.cz> --- include/linux/mm.h | 1 + mm/memory.c | 11 +++++++---- 2 files changed, 8 insertions(+), 4 deletions(-)
diff --git a/include/linux/mm.h b/include/linux/mm.h
index e03dd29..e04f531 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h@@ -208,6 +208,7 @@ struct vm_fault { pgoff_t pgoff; /* Logical page offset based on vma */ void __user *virtual_address; /* Faulting virtual address */ + struct page *cow_page; /* Handler may choose to COW */ struct page *page; /* ->fault handlers should return a * page here, unless VM_FAULT_NOPAGE * is set (which is also implied by
diff --git a/mm/memory.c b/mm/memory.c
index d67fd9f..42bf429 100644
--- a/mm/memory.c
+++ b/mm/memory.c@@ -2003,6 +2003,7 @@ static int do_page_mkwrite(struct vm_area_struct *vma, struct page *page, vmf.pgoff = page->index; vmf.flags = FAULT_FLAG_WRITE|FAULT_FLAG_MKWRITE; vmf.page = page; + vmf.cow_page = NULL; ret = vma->vm_ops->page_mkwrite(vma, &vmf); if (unlikely(ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE)))
@@ -2689,7 +2690,8 @@ oom: } static int __do_fault(struct vm_area_struct *vma, unsigned long address, - pgoff_t pgoff, unsigned int flags, struct page **page) + pgoff_t pgoff, unsigned int flags, + struct page *cow_page, struct page **page) { struct vm_fault vmf; int ret;
@@ -2698,6 +2700,7 @@ static int __do_fault(struct vm_area_struct *vma, unsigned long address, vmf.pgoff = pgoff; vmf.flags = flags; vmf.page = NULL; + vmf.cow_page = cow_page; ret = vma->vm_ops->fault(vma, &vmf); if (unlikely(ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE | VM_FAULT_RETRY)))
@@ -2890,7 +2893,7 @@ static int do_read_fault(struct mm_struct *mm, struct vm_area_struct *vma, pte_unmap_unlock(pte, ptl); } - ret = __do_fault(vma, address, pgoff, flags, &fault_page); + ret = __do_fault(vma, address, pgoff, flags, NULL, &fault_page); if (unlikely(ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE | VM_FAULT_RETRY))) return ret;
@@ -2929,7 +2932,7 @@ static int do_cow_fault(struct mm_struct *mm, struct vm_area_struct *vma, return VM_FAULT_OOM; } - ret = __do_fault(vma, address, pgoff, flags, &fault_page); + ret = __do_fault(vma, address, pgoff, flags, new_page, &fault_page); if (unlikely(ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE | VM_FAULT_RETRY))) goto uncharge_out;
@@ -2965,7 +2968,7 @@ static int do_shared_fault(struct mm_struct *mm, struct vm_area_struct *vma, int dirtied = 0; int ret, tmp; - ret = __do_fault(vma, address, pgoff, flags, &fault_page); + ret = __do_fault(vma, address, pgoff, flags, NULL, &fault_page); if (unlikely(ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE | VM_FAULT_RETRY))) return ret;
--
2.0.0
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