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authorMatthew Wilcox <matthew.r.wilcox@intel.com>2015-02-16 23:58:50 (GMT)
committerLinus Torvalds <torvalds@linux-foundation.org>2015-02-17 01:56:03 (GMT)
commit2e4cdab0584fa884e0a81c4f45b93ce875c9fcaa (patch)
treec20a4224ed2ac8d5e9416c7fcc451cc144025626 /mm
parent283307c7607de2a06d3bfae4cfbf5a566d457090 (diff)
mm: allow page fault handlers to perform the COW
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. The handler cannot insert the page itself if there is already a read-only mapping at that address, so allow the handler to return VM_FAULT_LOCKED and set the fault_page to be NULL. This indicates to the MM code that the i_mmap_lock is held instead of the page lock. Signed-off-by: Matthew Wilcox <matthew.r.wilcox@intel.com> Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Andreas Dilger <andreas.dilger@intel.com> Cc: Boaz Harrosh <boaz@plexistor.com> Cc: Christoph Hellwig <hch@lst.de> Cc: Dave Chinner <david@fromorbit.com> Cc: Jan Kara <jack@suse.cz> Cc: Jens Axboe <axboe@kernel.dk> Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Cc: Randy Dunlap <rdunlap@infradead.org> Cc: Ross Zwisler <ross.zwisler@linux.intel.com> Cc: Theodore Ts'o <tytso@mit.edu> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm')
-rw-r--r--mm/memory.c41
1 files changed, 32 insertions, 9 deletions
diff --git a/mm/memory.c b/mm/memory.c
index 1b04e13..8068893 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1965,6 +1965,7 @@ 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)))
@@ -2639,7 +2640,8 @@ oom:
* See filemap_fault() and __lock_page_retry().
*/
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;
@@ -2648,10 +2650,13 @@ 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)))
return ret;
+ if (!vmf.page)
+ goto out;
if (unlikely(PageHWPoison(vmf.page))) {
if (ret & VM_FAULT_LOCKED)
@@ -2665,6 +2670,7 @@ static int __do_fault(struct vm_area_struct *vma, unsigned long address,
else
VM_BUG_ON_PAGE(!PageLocked(vmf.page), vmf.page);
+ out:
*page = vmf.page;
return ret;
}
@@ -2835,7 +2841,7 @@ 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;
@@ -2875,26 +2881,43 @@ 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;
- copy_user_highpage(new_page, fault_page, address, vma);
+ if (fault_page)
+ copy_user_highpage(new_page, fault_page, address, vma);
__SetPageUptodate(new_page);
pte = pte_offset_map_lock(mm, pmd, address, &ptl);
if (unlikely(!pte_same(*pte, orig_pte))) {
pte_unmap_unlock(pte, ptl);
- unlock_page(fault_page);
- page_cache_release(fault_page);
+ if (fault_page) {
+ unlock_page(fault_page);
+ page_cache_release(fault_page);
+ } else {
+ /*
+ * The fault handler has no page to lock, so it holds
+ * i_mmap_lock for read to protect against truncate.
+ */
+ i_mmap_unlock_read(vma->vm_file->f_mapping);
+ }
goto uncharge_out;
}
do_set_pte(vma, address, new_page, pte, true, true);
mem_cgroup_commit_charge(new_page, memcg, false);
lru_cache_add_active_or_unevictable(new_page, vma);
pte_unmap_unlock(pte, ptl);
- unlock_page(fault_page);
- page_cache_release(fault_page);
+ if (fault_page) {
+ unlock_page(fault_page);
+ page_cache_release(fault_page);
+ } else {
+ /*
+ * The fault handler has no page to lock, so it holds
+ * i_mmap_lock for read to protect against truncate.
+ */
+ i_mmap_unlock_read(vma->vm_file->f_mapping);
+ }
return ret;
uncharge_out:
mem_cgroup_cancel_charge(new_page, memcg);
@@ -2913,7 +2936,7 @@ 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;

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