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mm: remove optimizations based on i_size in mapping writeback waits 

Marcelo added this i_size based optimization with a patch in 2004
(commitid is from the linux-history tree):

    commit 765dad09b4ac101a32d87af2bb793c3060497d3c
    Author: Marcelo Tosatti <marcelo.tosatti@cyclades.com>
    Date:   Tue Sep 7 17:51:17 2004 -0700

	small wait_on_page_writeback_range() optimization

	filemap_fdatawait() calls wait_on_page_writeback_range() with -1
	as "end" parameter.  This is not needed since we know the EOF
	from the inode.  Use that instead.

There may be races here, particularly with clustered or network
filesystems. It also seems like a bit of a layering violation since
we're operating on an address_space here, not an inode.

Finally, it's also questionable whether this optimization really helps
on workloads that we care about. Should we be optimizing for writeback
vs. truncate races in a codepath where we expect to wait anyway? It
doesn't seem worth the risk.

Remove this optimization from the filemap_fdatawait codepaths. This
means that filemap_fdatawait becomes a trivial wrapper around
filemap_fdatawait_range.

Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Jeff Layton <jlayton@redhat.com>
This commit is contained in:
Jeff Layton 2017-07-31 10:29:38 -04:00
parent 3b49c9a1e9
commit ffb959bbdf
2 changed files with 7 additions and 30 deletions
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7
include/linux/fs.h
View File

@ -2538,10 +2538,15 @@ extern int invalidate_inode_pages2_range(struct address_space *mapping,
extern int write_inode_now(struct inode *, int);
extern int filemap_fdatawrite(struct address_space *);
extern int filemap_flush(struct address_space *);
extern int filemap_fdatawait(struct address_space *);
extern int filemap_fdatawait_keep_errors(struct address_space *mapping);
extern int filemap_fdatawait_range(struct address_space *, loff_t lstart,
loff_t lend);
static inline int filemap_fdatawait(struct address_space *mapping)
{
return filemap_fdatawait_range(mapping, 0, LLONG_MAX);
}
extern bool filemap_range_has_page(struct address_space *, loff_t lstart,
loff_t lend);
extern int __must_check file_fdatawait_range(struct file *file, loff_t lstart,

30
mm/filemap.c
View File

@ -512,39 +512,11 @@ EXPORT_SYMBOL(file_fdatawait_range);
*/
int filemap_fdatawait_keep_errors(struct address_space *mapping)
{
loff_t i_size = i_size_read(mapping->host);
if (i_size == 0)
return 0;
__filemap_fdatawait_range(mapping, 0, i_size - 1);
__filemap_fdatawait_range(mapping, 0, LLONG_MAX);
return filemap_check_and_keep_errors(mapping);
}
EXPORT_SYMBOL(filemap_fdatawait_keep_errors);
/**
* filemap_fdatawait - wait for all under-writeback pages to complete
* @mapping: address space structure to wait for
*
* Walk the list of under-writeback pages of the given address space
* and wait for all of them. Check error status of the address space
* and return it.
*
* Since the error status of the address space is cleared by this function,
* callers are responsible for checking the return value and handling and/or
* reporting the error.
*/
int filemap_fdatawait(struct address_space *mapping)
{
loff_t i_size = i_size_read(mapping->host);
if (i_size == 0)
return 0;
return filemap_fdatawait_range(mapping, 0, i_size - 1);
}
EXPORT_SYMBOL(filemap_fdatawait);
static bool mapping_needs_writeback(struct address_space *mapping)
{
return (!dax_mapping(mapping) && mapping->nrpages) ||