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iomap: factor out a iomap_writepage_handle_eof helper 

Most of iomap_do_writepage is dedidcated to handling a folio crossing or
beyond i_size.  Split this is into a separate helper and update the
commens to deal with folios instead of pages and make them more readable.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20231207072710.176093-6-hch@lst.de
Reviewed-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Christian Brauner <brauner@kernel.org>
This commit is contained in:
Christoph Hellwig 2023-12-07 08:27:01 +01:00 committed by Christian Brauner
parent c2dc7e5589
commit e3a491a26b
1 changed files with 62 additions and 66 deletions
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128
fs/iomap/buffered-io.c
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@ -1758,6 +1758,64 @@ iomap_add_to_ioend(struct inode *inode, loff_t pos, struct folio *folio,
wbc_account_cgroup_owner(wbc, &folio->page, len);
}
/*
* Check interaction of the folio with the file end.
*
* If the folio is entirely beyond i_size, return false. If it straddles
* i_size, adjust end_pos and zero all data beyond i_size.
*/
static bool iomap_writepage_handle_eof(struct folio *folio, struct inode *inode,
u64 *end_pos)
{
u64 isize = i_size_read(inode);
if (*end_pos > isize) {
size_t poff = offset_in_folio(folio, isize);
pgoff_t end_index = isize >> PAGE_SHIFT;
/*
* If the folio is entirely ouside of i_size, skip it.
*
* This can happen due to a truncate operation that is in
* progress and in that case truncate will finish it off once
* we've dropped the folio lock.
*
* Note that the pgoff_t used for end_index is an unsigned long.
* If the given offset is greater than 16TB on a 32-bit system,
* then if we checked if the folio is fully outside i_size with
* "if (folio->index >= end_index + 1)", "end_index + 1" would
* overflow and evaluate to 0. Hence this folio would be
* redirtied and written out repeatedly, which would result in
* an infinite loop; the user program performing this operation
* would hang. Instead, we can detect this situation by
* checking if the folio is totally beyond i_size or if its
* offset is just equal to the EOF.
*/
if (folio->index > end_index ||
(folio->index == end_index && poff == 0))
return false;
/*
* The folio straddles i_size.
*
* It must be zeroed out on each and every writepage invocation
* because it may be mmapped:
*
* A file is mapped in multiples of the page size. For a
* file that is not a multiple of the page size, the
* remaining memory is zeroed when mapped, and writes to that
* region are not written out to the file.
*
* Also adjust the writeback range to skip all blocks entirely
* beyond i_size.
*/
folio_zero_segment(folio, poff, folio_size(folio));
*end_pos = isize;
}
return true;
}
/*
* We implement an immediate ioend submission policy here to avoid needing to
* chain multiple ioends and hence nest mempool allocations which can violate
@ -1898,78 +1956,16 @@ static int iomap_do_writepage(struct folio *folio,
{
struct iomap_writepage_ctx *wpc = data;
struct inode *inode = folio->mapping->host;
u64 end_pos, isize;
u64 end_pos = folio_pos(folio) + folio_size(folio);
trace_iomap_writepage(inode, folio_pos(folio), folio_size(folio));
/*
* Is this folio beyond the end of the file?
*
* The folio index is less than the end_index, adjust the end_pos
* to the highest offset that this folio should represent.
* -----------------------------------------------------
* | file mapping | <EOF> |
* -----------------------------------------------------
* | Page ... | Page N-2 | Page N-1 | Page N | |
* ^--------------------------------^----------|--------
* | desired writeback range | see else |
* ---------------------------------^------------------|
*/
isize = i_size_read(inode);
end_pos = folio_pos(folio) + folio_size(folio);
if (end_pos > isize) {
/*
* Check whether the page to write out is beyond or straddles
* i_size or not.
* -------------------------------------------------------
* | file mapping | <EOF> |
* -------------------------------------------------------
* | Page ... | Page N-2 | Page N-1 | Page N | Beyond |
* ^--------------------------------^-----------|---------
* | | Straddles |
* ---------------------------------^-----------|--------|
*/
size_t poff = offset_in_folio(folio, isize);
pgoff_t end_index = isize >> PAGE_SHIFT;
/*
* Skip the page if it's fully outside i_size, e.g.
* due to a truncate operation that's in progress. We've
* cleaned this page and truncate will finish things off for
* us.
*
* Note that the end_index is unsigned long. If the given
* offset is greater than 16TB on a 32-bit system then if we
* checked if the page is fully outside i_size with
* "if (page->index >= end_index + 1)", "end_index + 1" would
* overflow and evaluate to 0. Hence this page would be
* redirtied and written out repeatedly, which would result in
* an infinite loop; the user program performing this operation
* would hang. Instead, we can detect this situation by
* checking if the page is totally beyond i_size or if its
* offset is just equal to the EOF.
*/
if (folio->index > end_index ||
(folio->index == end_index && poff == 0))
goto unlock;
/*
* The page straddles i_size. It must be zeroed out on each
* and every writepage invocation because it may be mmapped.
* "A file is mapped in multiples of the page size. For a file
* that is not a multiple of the page size, the remaining
* memory is zeroed when mapped, and writes to that region are
* not written out to the file."
*/
folio_zero_segment(folio, poff, folio_size(folio));
end_pos = isize;
if (!iomap_writepage_handle_eof(folio, inode, &end_pos)) {
folio_unlock(folio);
return 0;
}
return iomap_writepage_map(wpc, wbc, inode, folio, end_pos);
unlock:
folio_unlock(folio);
return 0;
}
int