Re: [PATCH v5 06/12] Add get_user_pages() variant that fails if major fault is required.

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 On 07/19/2010 06:30 PM, Gleb Natapov wrote:
This patch add get_user_pages() variant that only succeeds if getting
a reference to a page doesn't require major fault.



Andrew, can this go in through kvm.git?

Reviewed-by: Rik van Riel<riel@xxxxxxxxxx>
Signed-off-by: Gleb Natapov<gleb@xxxxxxxxxx>
---
  fs/ncpfs/mmap.c    |    2 ++
  include/linux/mm.h |    5 +++++
  mm/filemap.c       |    3 +++
  mm/memory.c        |   31 ++++++++++++++++++++++++++++---
  mm/shmem.c         |    8 +++++++-
  5 files changed, 45 insertions(+), 4 deletions(-)

diff --git a/fs/ncpfs/mmap.c b/fs/ncpfs/mmap.c
index 56f5b3a..b9c4f36 100644
--- a/fs/ncpfs/mmap.c
+++ b/fs/ncpfs/mmap.c
@@ -39,6 +39,8 @@ static int ncp_file_mmap_fault(struct vm_area_struct *area,
  	int bufsize;
  	int pos; /* XXX: loff_t ? */

+	if (vmf->flags&  FAULT_FLAG_MINOR)
+		return VM_FAULT_MAJOR | VM_FAULT_ERROR;
  	/*
  	 * ncpfs has nothing against high pages as long
  	 * as recvmsg and memset works on it
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 4238a9c..2bfc85a 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -140,6 +140,7 @@ extern pgprot_t protection_map[16];
  #define FAULT_FLAG_WRITE	0x01	/* Fault was a write access */
  #define FAULT_FLAG_NONLINEAR	0x02	/* Fault was via a nonlinear mapping */
  #define FAULT_FLAG_MKWRITE	0x04	/* Fault was mkwrite of existing pte */
+#define FAULT_FLAG_MINOR	0x08	/* Do only minor fault */

  /*
   * This interface is used by x86 PAT code to identify a pfn mapping that is
@@ -843,6 +844,9 @@ extern int access_process_vm(struct task_struct *tsk, unsigned long addr, void *
  int get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
  			unsigned long start, int nr_pages, int write, int force,
  			struct page **pages, struct vm_area_struct **vmas);
+int get_user_pages_noio(struct task_struct *tsk, struct mm_struct *mm,
+			unsigned long start, int nr_pages, int write, int force,
+			struct page **pages, struct vm_area_struct **vmas);
  int get_user_pages_fast(unsigned long start, int nr_pages, int write,
  			struct page **pages);
  struct page *get_dump_page(unsigned long addr);
@@ -1373,6 +1377,7 @@ struct page *follow_page(struct vm_area_struct *, unsigned long address,
  #define FOLL_GET	0x04	/* do get_page on page */
  #define FOLL_DUMP	0x08	/* give error on hole if it would be zero */
  #define FOLL_FORCE	0x10	/* get_user_pages read/write w/o permission */
+#define FOLL_MINOR	0x20	/* do only minor page faults */

  typedef int (*pte_fn_t)(pte_t *pte, pgtable_t token, unsigned long addr,
  			void *data);
diff --git a/mm/filemap.c b/mm/filemap.c
index 20e5642..1186338 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1548,6 +1548,9 @@ int filemap_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
  			goto no_cached_page;
  		}
  	} else {
+		if (vmf->flags&  FAULT_FLAG_MINOR)
+			return VM_FAULT_MAJOR | VM_FAULT_ERROR;
+
  		/* No page in the page cache at all */
  		do_sync_mmap_readahead(vma, ra, file, offset);
  		count_vm_event(PGMAJFAULT);
diff --git a/mm/memory.c b/mm/memory.c
index 119b7cc..7dfaba2 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1433,10 +1433,13 @@ int __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
  			cond_resched();
  			while (!(page = follow_page(vma, start, foll_flags))) {
  				int ret;
+				unsigned int fault_fl =
+					((foll_flags&  FOLL_WRITE) ?
+					FAULT_FLAG_WRITE : 0) |
+					((foll_flags&  FOLL_MINOR) ?
+					FAULT_FLAG_MINOR : 0);

-				ret = handle_mm_fault(mm, vma, start,
-					(foll_flags&  FOLL_WRITE) ?
-					FAULT_FLAG_WRITE : 0);
+				ret = handle_mm_fault(mm, vma, start, fault_fl);

  				if (ret&  VM_FAULT_ERROR) {
  					if (ret&  VM_FAULT_OOM)
@@ -1444,6 +1447,8 @@ int __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
  					if (ret&
  					(VM_FAULT_HWPOISON|VM_FAULT_SIGBUS))
  						return i ? i : -EFAULT;
+					else if (ret&  VM_FAULT_MAJOR)
+						return i ? i : -EFAULT;
  					BUG();
  				}
  				if (ret&  VM_FAULT_MAJOR)
@@ -1554,6 +1559,23 @@ int get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
  }
  EXPORT_SYMBOL(get_user_pages);

+int get_user_pages_noio(struct task_struct *tsk, struct mm_struct *mm,
+		unsigned long start, int nr_pages, int write, int force,
+		struct page **pages, struct vm_area_struct **vmas)
+{
+	int flags = FOLL_TOUCH | FOLL_MINOR;
+
+	if (pages)
+		flags |= FOLL_GET;
+	if (write)
+		flags |= FOLL_WRITE;
+	if (force)
+		flags |= FOLL_FORCE;
+
+	return __get_user_pages(tsk, mm, start, nr_pages, flags, pages, vmas);
+}
+EXPORT_SYMBOL(get_user_pages_noio);
+
  /**
   * get_dump_page() - pin user page in memory while writing it to core dump
   * @addr: user address
@@ -2640,6 +2662,9 @@ static int do_swap_page(struct mm_struct *mm, struct vm_area_struct *vma,
  	delayacct_set_flag(DELAYACCT_PF_SWAPIN);
  	page = lookup_swap_cache(entry);
  	if (!page) {
+		if (flags&  FAULT_FLAG_MINOR)
+			return VM_FAULT_MAJOR | VM_FAULT_ERROR;
+
  		grab_swap_token(mm); /* Contend for token _before_ read-in */
  		page = swapin_readahead(entry,
  					GFP_HIGHUSER_MOVABLE, vma, address);
diff --git a/mm/shmem.c b/mm/shmem.c
index f65f840..acc8958 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -1227,6 +1227,7 @@ static int shmem_getpage(struct inode *inode, unsigned long idx,
  	swp_entry_t swap;
  	gfp_t gfp;
  	int error;
+	int flags = type ? *type : 0;

  	if (idx>= SHMEM_MAX_INDEX)
  		return -EFBIG;
@@ -1275,6 +1276,11 @@ repeat:
  		swappage = lookup_swap_cache(swap);
  		if (!swappage) {
  			shmem_swp_unmap(entry);
+			if (flags&  FAULT_FLAG_MINOR) {
+				spin_unlock(&info->lock);
+				*type = VM_FAULT_MAJOR | VM_FAULT_ERROR;
+				goto failed;
+			}
  			/* here we actually do the io */
  			if (type&&  !(*type&  VM_FAULT_MAJOR)) {
  				__count_vm_event(PGMAJFAULT);
@@ -1483,7 +1489,7 @@ static int shmem_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
  {
  	struct inode *inode = vma->vm_file->f_path.dentry->d_inode;
  	int error;
-	int ret;
+	int ret = (int)vmf->flags;

  	if (((loff_t)vmf->pgoff<<  PAGE_CACHE_SHIFT)>= i_size_read(inode))
  		return VM_FAULT_SIGBUS;


--
error compiling committee.c: too many arguments to function

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