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

[Avi Kivity <avi@redhat.com>]

  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@redhat.com>
> Signed-off-by: Gleb Natapov<gleb@redhat.com>
> ---
>   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

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>