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Date: Wed, 21 Feb 2007 13:07:03 -0500
From: Peter Staubach <staubach@...hat.com>
To: Miklos Szeredi <miklos@...redi.hu>
CC: akpm@...ux-foundation.org, hugh@...itas.com,
linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH] update ctime and mtime for mmaped write
Miklos Szeredi wrote:
> From: Miklos Szeredi <mszeredi@...e.cz>
>
> This patch makes writing to shared memory mappings update st_ctime and
> st_mtime as defined by SUSv3:
>
> The st_ctime and st_mtime fields of a file that is mapped with
> MAP_SHARED and PROT_WRITE shall be marked for update at some point
> in the interval between a write reference to the mapped region and
> the next call to msync() with MS_ASYNC or MS_SYNC for that portion
> of the file by any process. If there is no such call and if the
> underlying file is modified as a result of a write reference, then
> these fields shall be marked for update at some time after the
> write reference.
>
> A new address_space flag is introduced: AS_CMTIME. This is set each
> time a page is dirtied through a userspace memory mapping. This
> includes write accesses via get_user_pages().
>
> Note, the flag is set unconditionally, even if the page is already
> dirty. This is important, because the page might have been dirtied
> earlier by a non-mmap write.
>
> This flag is checked in msync() and __fput(), and if set, the file
> times are updated and the flag is cleared
>
> The flag is also cleared, if the time update is triggered by a normal
> write. This is not mandated by the standard, but seems to be a sane
> thing to do.
>
> Fixes Novell Bugzilla #206431.
>
> Inspired by Peter Staubach's patch and the resulting comments.
>
>
An updated version of the original patch was submitted to LKML
yesterday... :-)
Some comments below --
> Signed-off-by: Miklos Szeredi <mszeredi@...e.cz>
> ---
>
> Index: linux/include/linux/pagemap.h
> ===================================================================
> --- linux.orig/include/linux/pagemap.h 2007-02-21 14:15:06.000000000 +0100
> +++ linux/include/linux/pagemap.h 2007-02-21 14:16:04.000000000 +0100
> @@ -18,6 +18,7 @@
> */
> #define AS_EIO (__GFP_BITS_SHIFT + 0) /* IO error on async write */
> #define AS_ENOSPC (__GFP_BITS_SHIFT + 1) /* ENOSPC on async write */
> +#define AS_CMTIME (__GFP_BITS_SHIFT + 2) /* ctime/mtime update needed */
>
> static inline gfp_t mapping_gfp_mask(struct address_space * mapping)
> {
> Index: linux/mm/msync.c
> ===================================================================
> --- linux.orig/mm/msync.c 2007-02-21 14:14:43.000000000 +0100
> +++ linux/mm/msync.c 2007-02-21 14:16:04.000000000 +0100
> @@ -77,6 +77,7 @@ asmlinkage long sys_msync(unsigned long
> }
> file = vma->vm_file;
> start = vma->vm_end;
> + mapping_update_time(file);
> if ((flags & MS_SYNC) && file &&
> (vma->vm_flags & VM_SHARED)) {
> get_file(file);
>
It seems to me that this might lead to file times being updated for
non-MAP_SHARED mappings.
> Index: linux/fs/file_table.c
> ===================================================================
> --- linux.orig/fs/file_table.c 2007-02-21 14:14:43.000000000 +0100
> +++ linux/fs/file_table.c 2007-02-21 14:16:04.000000000 +0100
> @@ -165,6 +165,7 @@ void fastcall __fput(struct file *file)
> */
> eventpoll_release(file);
> locks_remove_flock(file);
> + mapping_update_time(file);
>
> if (file->f_op && file->f_op->release)
> file->f_op->release(inode, file);
> Index: linux/fs/inode.c
> ===================================================================
> --- linux.orig/fs/inode.c 2007-02-21 14:14:43.000000000 +0100
> +++ linux/fs/inode.c 2007-02-21 14:16:04.000000000 +0100
> @@ -1219,6 +1219,7 @@ void file_update_time(struct file *file)
> struct timespec now;
> int sync_it = 0;
>
> + clear_bit(AS_CMTIME, &file->f_mapping->flags);
> if (IS_NOCMTIME(inode))
> return;
> if (IS_RDONLY(inode))
> @@ -1241,6 +1242,12 @@ void file_update_time(struct file *file)
>
> EXPORT_SYMBOL(file_update_time);
>
> +void mapping_update_time(struct file *file)
> +{
> + if (test_bit(AS_CMTIME, &file->f_mapping->flags))
> + file_update_time(file);
> +}
> +
> int inode_needs_sync(struct inode *inode)
> {
> if (IS_SYNC(inode))
> Index: linux/include/linux/fs.h
> ===================================================================
> --- linux.orig/include/linux/fs.h 2007-02-21 14:15:06.000000000 +0100
> +++ linux/include/linux/fs.h 2007-02-21 14:16:04.000000000 +0100
> @@ -1887,6 +1887,7 @@ extern int inode_change_ok(struct inode
> extern int __must_check inode_setattr(struct inode *, struct iattr *);
>
> extern void file_update_time(struct file *file);
> +extern void mapping_update_time(struct file *file);
>
> static inline ino_t parent_ino(struct dentry *dentry)
> {
> Index: linux/include/linux/mm.h
> ===================================================================
> --- linux.orig/include/linux/mm.h 2007-02-21 14:14:43.000000000 +0100
> +++ linux/include/linux/mm.h 2007-02-21 14:16:04.000000000 +0100
> @@ -790,6 +790,7 @@ int redirty_page_for_writepage(struct wr
> struct page *page);
> int FASTCALL(set_page_dirty(struct page *page));
> int set_page_dirty_lock(struct page *page);
> +int set_page_dirty_mapping(struct page *page);
>
This aspect of the design seems intrusive to me. I didn't see a strong
reason to introduce new versions of many of the routines just to handle
these semantics. What motivated this part of your design? Why the new
_mapping versions of routines?
Thanx...
ps
> int clear_page_dirty_for_io(struct page *page);
>
> extern unsigned long do_mremap(unsigned long addr,
> Index: linux/mm/memory.c
> ===================================================================
> --- linux.orig/mm/memory.c 2007-02-21 14:15:06.000000000 +0100
> +++ linux/mm/memory.c 2007-02-21 14:16:04.000000000 +0100
> @@ -676,7 +676,7 @@ static unsigned long zap_pte_range(struc
> anon_rss--;
> else {
> if (pte_dirty(ptent))
> - set_page_dirty(page);
> + set_page_dirty_mapping(page);
> if (pte_young(ptent))
> mark_page_accessed(page);
> file_rss--;
> @@ -954,7 +954,7 @@ struct page *follow_page(struct vm_area_
> if (flags & FOLL_TOUCH) {
> if ((flags & FOLL_WRITE) &&
> !pte_dirty(pte) && !PageDirty(page))
> - set_page_dirty(page);
> + set_page_dirty_mapping(page);
> mark_page_accessed(page);
> }
> unlock:
> @@ -1469,6 +1469,15 @@ static inline void cow_user_page(struct
> copy_user_highpage(dst, src, va, vma);
> }
>
> +static void set_page_dirty_mapping_balance(struct page *page)
> +{
> + if (set_page_dirty_mapping(page)) {
> + struct address_space *mapping = page_mapping(page);
> + if (mapping)
> + balance_dirty_pages_ratelimited(mapping);
> + }
> +}
> +
> /*
> * This routine handles present pages, when users try to write
> * to a shared page. It is done by copying the page to a new address
> @@ -1620,7 +1629,7 @@ gotten:
> unlock:
> pte_unmap_unlock(page_table, ptl);
> if (dirty_page) {
> - set_page_dirty_balance(dirty_page);
> + set_page_dirty_mapping_balance(dirty_page);
> put_page(dirty_page);
> }
> return ret;
> @@ -2274,7 +2283,7 @@ retry:
> unlock:
> pte_unmap_unlock(page_table, ptl);
> if (dirty_page) {
> - set_page_dirty_balance(dirty_page);
> + set_page_dirty_mapping_balance(dirty_page);
> put_page(dirty_page);
> }
> return ret;
> Index: linux/mm/page-writeback.c
> ===================================================================
> --- linux.orig/mm/page-writeback.c 2007-02-21 14:15:54.000000000 +0100
> +++ linux/mm/page-writeback.c 2007-02-21 14:16:04.000000000 +0100
> @@ -244,16 +244,6 @@ static void balance_dirty_pages(struct a
> pdflush_operation(background_writeout, 0);
> }
>
> -void set_page_dirty_balance(struct page *page)
> -{
> - if (set_page_dirty(page)) {
> - struct address_space *mapping = page_mapping(page);
> -
> - if (mapping)
> - balance_dirty_pages_ratelimited(mapping);
> - }
> -}
> -
> /**
> * balance_dirty_pages_ratelimited_nr - balance dirty memory state
> * @mapping: address_space which was dirtied
> @@ -819,6 +809,30 @@ int fastcall set_page_dirty(struct page
> EXPORT_SYMBOL(set_page_dirty);
>
> /*
> + * Special set_page_dirty() variant for dirtiness coming from a memory
> + * mapping. In this case the ctime/mtime update flag needs to be set.
> + */
> +int set_page_dirty_mapping(struct page *page)
> +{
> + struct address_space *mapping = page_mapping(page);
> +
> + if (likely(mapping)) {
> + int (*spd)(struct page *) = mapping->a_ops->set_page_dirty;
> +#ifdef CONFIG_BLOCK
> + if (!spd)
> + spd = __set_page_dirty_buffers;
> +#endif
> + set_bit(AS_CMTIME, &mapping->flags);
> + return (*spd)(page);
> + }
> + if (!PageDirty(page)) {
> + if (!TestSetPageDirty(page))
> + return 1;
> + }
> + return 0;
> +}
> +
> +/*
> * set_page_dirty() is racy if the caller has no reference against
> * page->mapping->host, and if the page is unlocked. This is because another
> * CPU could truncate the page off the mapping and then free the mapping.
> Index: linux/mm/rmap.c
> ===================================================================
> --- linux.orig/mm/rmap.c 2007-02-21 14:14:43.000000000 +0100
> +++ linux/mm/rmap.c 2007-02-21 14:16:04.000000000 +0100
> @@ -598,7 +598,7 @@ void page_remove_rmap(struct page *page,
> * faster for those pages still in swapcache.
> */
> if (page_test_and_clear_dirty(page))
> - set_page_dirty(page);
> + set_page_dirty_mapping(page);
> __dec_zone_page_state(page,
> PageAnon(page) ? NR_ANON_PAGES : NR_FILE_MAPPED);
> }
> @@ -643,7 +643,7 @@ static int try_to_unmap_one(struct page
>
> /* Move the dirty bit to the physical page now the pte is gone. */
> if (pte_dirty(pteval))
> - set_page_dirty(page);
> + set_page_dirty_mapping(page);
>
> /* Update high watermark before we lower rss */
> update_hiwater_rss(mm);
> @@ -777,7 +777,7 @@ static void try_to_unmap_cluster(unsigne
>
> /* Move the dirty bit to the physical page now the pte is gone. */
> if (pte_dirty(pteval))
> - set_page_dirty(page);
> + set_page_dirty_mapping(page);
>
> page_remove_rmap(page, vma);
> page_cache_release(page);
> Index: linux/include/linux/writeback.h
> ===================================================================
> --- linux.orig/include/linux/writeback.h 2007-02-21 14:15:05.000000000 +0100
> +++ linux/include/linux/writeback.h 2007-02-21 14:16:04.000000000 +0100
> @@ -117,7 +117,6 @@ int sync_page_range(struct inode *inode,
> loff_t pos, loff_t count);
> int sync_page_range_nolock(struct inode *inode, struct address_space *mapping,
> loff_t pos, loff_t count);
> -void set_page_dirty_balance(struct page *page);
> void writeback_set_ratelimit(void);
>
> /* pdflush.c */
>
-
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