xfs: get rid of xfs_cluster_write()
v2 cover xfs: get rid of xfs_cluster_write()
Hi folks,
This is the second version of the patchset that removes xfs_cluster_write() in preference to using state in generic_writepages to enable clustering of pages. The full description from the v1 patchset is here:
http://oss.sgi.com/archives/xfs/2015-08/msg00224.html
The end result is effectively unchanged from version 1, just the breakdown of the patches is different to the original posting, as requested by Christoph.
-Dave.
Version 2:
- promote removal of non-blocking behaviour to be an initial cleanup patch
- collapse staged introduction of struct xfs_writepage_context into a single patch.
_______________________________________________
xfs mailing list
[email protected]
http://oss.sgi.com/mailman/listinfo/xfs
PATCH v2 1/4 xfs: remove nonblocking mode from xfs_vm_writepage
From: Dave Chinner <[email protected]>
Remove the nonblocking optimisation done for mapping lookups during writeback. It's not clear that leaving a hole in the writeback range just because we couldn't get a lock is really a win, as it makes us do another small random IO later on rather than a large sequential IO now.
As this gets in the way of sane error handling later on, just remove for the moment and we can re-introduce an equivalent optimisation in future if we see problems due to extent map lock contention.
--- fs/xfs/xfs_aops.c | 20 +++----------------- 1 file changed, 3 insertions(+), 17 deletions(-)
fs/xfs/xfs_aops.c +3 -17
@@ -276,8 +276,7 @@ xfs_map_blocks(struct inode *inode, loff_t offset, struct xfs_bmbt_irec *imap, - int type, - int nonblocking) + int type) { struct xfs_inode *ip = XFS_I(inode);struct xfs_mount *mp = ip->i_mount;
@@ -293,12 +292,7 @@ xfs_map_blocks(if (type ==XFS_IO_UNWRITTEN ) bmapi_flags |=XFS_BMAPI_IGSTATE ; -if (!xfs_ilock_nowait (ip,XFS_ILOCK_SHARED )) { -if (nonblocking) -return -EAGAIN ; -xfs_ilock (ip,XFS_ILOCK_SHARED ); - } - +xfs_ilock (ip,XFS_ILOCK_SHARED );ASSERT (ip->i_d.di_format !=XFS_DINODE_FMT_BTREE || (ip->i_df.if_flags &XFS_IFEXTENTS ));ASSERT (offset <= mp->m_super->s_maxbytes);
@@ -949,7 +943,6 @@ xfs_vm_writepage(ssize_t len;int err, imap_valid =0 , uptodate =1 ;int count =0 ; -int nonblocking =0 ;trace_xfs_writepage (inode, page,0 ,0 );
@@ -1049,9 +1042,6 @@ xfs_vm_writepage( offset =page_offset (page); type =XFS_IO_OVERWRITE ; -if (wbc->sync_mode ==WB_SYNC_NONE ) - nonblocking =1 ; - do { int new_ioend = 0;
@@ -1111,8 +1101,7 @@ xfs_vm_writepage(* time. */ new_ioend =1 ; - err =xfs_map_blocks (inode, offset, &imap, type, - nonblocking); + err =xfs_map_blocks (inode, offset, &imap, type);if (err) goto error; imap_valid =xfs_imap_valid (inode, &imap, offset);
@@ -1182,9 +1171,6 @@ error:if (iohead)xfs_cancel_ioend (iohead); -if (err == -EAGAIN ) - goto redirty; -xfs_aops_discard_page (page);ClearPageUptodate (page);unlock_page (page);
Signature · 6 lines
2.5.0 _______________________________________________ xfs mailing list [email protected] http://oss.sgi.com/mailman/listinfo/xfs
Re: [PATCH 1/4] xfs: remove nonblocking mode from xfs_vm_writepage
Looks fine,
_______________________________________________
xfs mailing list
[email protected]
http://oss.sgi.com/mailman/listinfo/xfs
PATCH v2 2/4 xfs: Introduce writeback context for writepages
In reply to Dave ChinnerFrom: Dave Chinner <[email protected]>
xfs_vm_writepages() calls generic_writepages to writeback a range of a file, but then xfs_vm_writepage() clusters pages itself as it does not have any context it can pass between->writepage calls from __write_cache_pages().
Introduce a writeback context for xfs_vm_writepages() and call __write_cache_pages directly with our own writepage callback so that we can pass that context to each writepage invocation. This encapsulates the current mapping, whether it is valid or not, the current ioend and it's IO type and the ioend chain being built.
This requires us to move the ioend submission up to the level where the writepage context is declared. This does mean we do not submit IO until we packaged the entire writeback range, but with the block plugging in the writepages call this is the way IO is submitted, anyway.
It also means that we need to handle discontiguous page ranges. If the pages sent down by write_cache_pages to the writepage callback are discontiguous, we need to detect this and put each discontiguous page range into individual ioends. This is needed to ensure that the ioend accurately represents the range of the file that it covers so that file size updates during IO completion set the size correctly. Failure to take into account the discontiguous ranges results in files being too small when writeback patterns are non-sequential.
--- fs/xfs/xfs_aops.c | 277 ++++++++++++++++++++++++++++-------------------------- 1 file changed, 146 insertions(+), 131 deletions(-)
fs/xfs/xfs_aops.c +146 -131
@@ -36,6 +36,18 @@#include <linux/pagevec.h> #include <linux/writeback.h> +/* +* structure owned by writepages passed to individual writepage calls +*/ +struct xfs_writepage_ctx { +struct xfs_bmbt_irec imap; +bool imap_valid; +unsigned int io_type; +struct xfs_ioend *iohead; +struct xfs_ioend *ioend; +sector_t last_block; +}; + void xfs_count_page_state( struct page *page,
@@ -328,7 +340,7 @@ xfs_map_blocks(return 0 ; } -STATIC int +STATIC bool xfs_imap_valid( struct inode *inode, struct xfs_bmbt_irec *imap,
@@ -516,38 +528,6 @@ xfs_submit_ioend( }/* -* Cancel submission of all buffer_heads so far in this endio. -* Toss the endio too. Only ever called for the initial page -* in a writepage request, so only ever one page. -*/ -STATIC void -xfs_cancel_ioend ( -xfs_ioend_t *ioend) -{ -xfs_ioend_t *next; -struct buffer_head *bh, *next_bh; - -do { - next = ioend->io_list; - bh = ioend->io_buffer_head; -do { - next_bh = bh->b_private; -clear_buffer_async_write (bh); -/* -* The unwritten flag is cleared when added to the -* ioend. We're not submitting for I/O so mark the -* buffer unwritten again for next time around. -*/ -if (ioend->io_type ==XFS_IO_UNWRITTEN ) -set_buffer_unwritten (bh); -unlock_buffer (bh); - }while ((bh = next_bh) !=NULL ); - -mempool_free (ioend, xfs_ioend_pool); - }while ((ioend = next) !=NULL ); -} - -/* * Test to see if we've been building up a completion structure for * earlier buffers -- if so, we try to append to this ioend if we * can, otherwise we finish off any current ioend and start another.
@@ -558,29 +538,27 @@ xfs_add_to_ioend(struct inode *inode, struct buffer_head *bh, xfs_off_t offset, - unsigned int type, - xfs_ioend_t **result, - int need_ioend) + struct xfs_writepage_ctx *wpc) { - xfs_ioend_t *ioend = *result; - -if (!ioend || need_ioend || type != ioend->io_type) { -xfs_ioend_t *previous = *result; - - ioend =xfs_alloc_ioend (inode, type); - ioend->io_offset = offset; - ioend->io_buffer_head = bh; - ioend->io_buffer_tail = bh; -if (previous) - previous->io_list = ioend; - *result = ioend; + if (!wpc->ioend || wpc->io_type != wpc->ioend->io_type || + bh->b_blocknr != wpc->last_block + 1) { + struct xfs_ioend *new; + + new =xfs_alloc_ioend (inode, wpc->io_type); + new->io_offset = offset; + new->io_buffer_head = bh; + new->io_buffer_tail = bh; +if (wpc->ioend) + wpc->ioend->io_list = new; + wpc->ioend = new; } else { - ioend->io_buffer_tail->b_private = bh; - ioend->io_buffer_tail = bh; + wpc->ioend->io_buffer_tail->b_private = bh; + wpc->ioend->io_buffer_tail = bh; } bh->b_private =NULL ; - ioend->io_size += bh->b_size; + wpc->ioend->io_size += bh->b_size; + wpc->last_block = bh->b_blocknr; }STATIC void
@@ -677,17 +655,15 @@ xfs_convert_page(struct inode *inode, struct page *page, loff_t tindex, - struct xfs_bmbt_irec *imap, - xfs_ioend_t **ioendp, + struct xfs_writepage_ctx *wpc, struct writeback_control *wbc) { struct buffer_head *bh, *head;xfs_off_t end_offset;unsigned long p_offset; -unsigned int type;int len, page_dirty;int count =0 , done =0 , uptodate =1 ; -xfs_off_t offset =page_offset (page); +xfs_off_t offset =page_offset (page);if (page->index != tindex) goto fail;
@@ -697,7 +673,7 @@ xfs_convert_page( goto fail_unlock_page;if (page->mapping != inode->i_mapping) goto fail_unlock_page; -if (!xfs_check_page_type (page, (*ioendp)->io_type, false)) +if (!xfs_check_page_type (page, wpc->ioend->io_type, false)) goto fail_unlock_page;/*
@@ -733,7 +709,7 @@ xfs_convert_page(* writeback. Hence for more optimal IO patterns, we should always * avoid partial page writeback due to multiple mappings on a page here. */ -if (!xfs_imap_valid (inode, imap, end_offset)) +if (!xfs_imap_valid (inode, &wpc->imap, end_offset)) goto fail_unlock_page; len =1 << inode->i_blkbits;
@@ -765,23 +741,22 @@ xfs_convert_page(if (buffer_unwritten (bh) ||buffer_delay (bh) ||buffer_mapped (bh)) {if (buffer_unwritten (bh)) - type =XFS_IO_UNWRITTEN ; + wpc->io_type =XFS_IO_UNWRITTEN ;else if (buffer_delay (bh)) - type =XFS_IO_DELALLOC ; + wpc->io_type =XFS_IO_DELALLOC ;else - type =XFS_IO_OVERWRITE ; + wpc->io_type =XFS_IO_OVERWRITE ;/* * imap should always be valid because of the above * partial page end_offset check on the imap. */ -ASSERT (xfs_imap_valid (inode, imap, offset)); +ASSERT (xfs_imap_valid (inode, &wpc->imap, offset));lock_buffer (bh); -if (type !=XFS_IO_OVERWRITE ) -xfs_map_at_offset (inode, bh, imap, offset); -xfs_add_to_ioend (inode, bh, offset, type, - ioendp, done); +if (wpc->io_type !=XFS_IO_OVERWRITE ) +xfs_map_at_offset (inode, bh, &wpc->imap, offset); +xfs_add_to_ioend (inode, bh, offset, wpc); page_dirty--; count++;
@@ -816,8 +791,7 @@ STATIC voidxfs_cluster_write ( struct inode *inode, pgoff_t tindex, - struct xfs_bmbt_irec *imap, - xfs_ioend_t **ioendp, + struct xfs_writepage_ctx *wpc, struct writeback_control *wbc, pgoff_t tlast) {
@@ -833,7 +807,7 @@ xfs_cluster_write(for (i =0 ; i <pagevec_count (&pvec); i++) { done =xfs_convert_page (inode, pvec.pages[i], tindex++, - imap, ioendp, wbc); + wpc, wbc);if (done)break ; }
@@ -919,6 +893,27 @@ out_invalidate:return ; } +static int +xfs_writepage_submit ( +struct xfs_writepage_ctx *wpc, +struct writeback_control *wbc, +int status) +{ +struct blk_plug plug; + +/* Reserve log space if we might write beyond the on-disk inode size. */ +if (!status && wpc->ioend && wpc->ioend->io_type !=XFS_IO_UNWRITTEN && +xfs_ioend_is_append (wpc->ioend)) + status =xfs_setfilesize_trans_alloc (wpc->ioend); + +if (wpc->iohead) { +blk_start_plug (&plug); +xfs_submit_ioend (wbc, wpc->iohead, status); +blk_finish_plug (&plug); + } +return status; +} +/* * Write out a dirty page. *
@@ -928,20 +923,19 @@ out_invalidate:* For any other dirty buffer heads on the page we should flush them. */ STATIC int -xfs_vm_writepage ( +xfs_do_writepage (struct page *page, -struct writeback_control *wbc) +struct writeback_control *wbc, +void *data) { +struct xfs_writepage_ctx *wpc = data;struct inode *inode = page->mapping->host;struct buffer_head *bh, *head; -struct xfs_bmbt_irec imap; -xfs_ioend_t *ioend =NULL , *iohead =NULL ;loff_t offset; -unsigned int type;__uint64_t end_offset;pgoff_t end_index, last_index;ssize_t len; -int err, imap_valid =0 , uptodate =1 ; +int err, uptodate =1 ;int count =0 ;trace_xfs_writepage (inode, page,0 ,0 );
@@ -1040,11 +1034,8 @@ xfs_vm_writepage( bh = head =page_buffers (page); offset =page_offset (page); - type =XFS_IO_OVERWRITE ; do { - int new_ioend = 0; - if (offset >= end_offset) break; if (!buffer_uptodate(bh))
@@ -1057,24 +1048,24 @@ xfs_vm_writepage(* buffers covering holes here. */ if (!buffer_mapped (bh) &&buffer_uptodate (bh)) { - imap_valid =0 ; + wpc->imap_valid = false;continue ; }if (buffer_unwritten (bh)) { -if (type !=XFS_IO_UNWRITTEN ) { - type =XFS_IO_UNWRITTEN ; - imap_valid =0 ; +if (wpc->io_type !=XFS_IO_UNWRITTEN ) { + wpc->io_type =XFS_IO_UNWRITTEN ; + wpc->imap_valid = false; } }else if (buffer_delay (bh)) { -if (type !=XFS_IO_DELALLOC ) { - type =XFS_IO_DELALLOC ; - imap_valid =0 ; +if (wpc->io_type !=XFS_IO_DELALLOC ) { + wpc->io_type =XFS_IO_DELALLOC ; + wpc->imap_valid = false; } }else if (buffer_uptodate (bh)) { -if (type !=XFS_IO_OVERWRITE ) { - type =XFS_IO_OVERWRITE ; - imap_valid =0 ; +if (wpc->io_type !=XFS_IO_OVERWRITE ) { + wpc->io_type =XFS_IO_OVERWRITE ; + wpc->imap_valid = false; } }else {if (PageUptodate (page))
@@ -1085,38 +1076,31 @@ xfs_vm_writepage(* subsequent writeable buffers into a new * ioend. */ - imap_valid =0 ; + wpc->imap_valid = false;continue ; } -if (imap_valid) - imap_valid =xfs_imap_valid (inode, &imap, offset); -if (!imap_valid) { -/* -* If we didn't have a valid mapping then we need to -* put the new mapping into a separate ioend structure. -* This ensures non-contiguous extents always have -* separate ioends, which is particularly important -* for unwritten extent conversion at I/O completion -* time. -*/ - new_ioend =1 ; - err =xfs_map_blocks (inode, offset, &imap, type); +if (wpc->imap_valid) + wpc->imap_valid =xfs_imap_valid (inode, &wpc->imap, + offset); +if (!wpc->imap_valid) { + err =xfs_map_blocks (inode, offset, &wpc->imap, + wpc->io_type);if (err) goto error; - imap_valid =xfs_imap_valid (inode, &imap, offset); + wpc->imap_valid =xfs_imap_valid (inode, &wpc->imap, + offset); } -if (imap_valid) { +if (wpc->imap_valid) {lock_buffer (bh); -if (type !=XFS_IO_OVERWRITE ) -xfs_map_at_offset (inode, bh, &imap, offset); -xfs_add_to_ioend (inode, bh, offset, type, &ioend, - new_ioend); +if (wpc->io_type !=XFS_IO_OVERWRITE ) +xfs_map_at_offset (inode, bh, &wpc->imap, offset); +xfs_add_to_ioend (inode, bh, offset, wpc); count++; } -if (!iohead) - iohead = ioend; +if (!wpc->iohead) + wpc->iohead = wpc->ioend; }while (offset += len, ((bh = bh->b_this_page) != head));
@@ -1126,20 +1110,20 @@ xfs_vm_writepage(xfs_start_page_writeback (page,1 , count);/* if there is no IO to be submitted for this page, we are done */ -if (!ioend) +if (!count)return 0 ; -ASSERT (iohead); +ASSERT (wpc->iohead);/* * Any errors from this point onwards need tobe reported through the IO * completion path as we have marked the initial page as under writeback * and unlocked it. */ -if (imap_valid) { +if (wpc->imap_valid) {xfs_off_t end_index; - end_index = imap.br_startoff + imap.br_blockcount; + end_index = wpc->imap.br_startoff + wpc->imap.br_blockcount;/* to bytes */ end_index <<= inode->i_blkbits;
@@ -1151,29 +1135,36 @@ xfs_vm_writepage(if (end_index > last_index) end_index = last_index; -xfs_cluster_write (inode, page->index +1 , &imap, &ioend, - wbc, end_index); +xfs_cluster_write (inode, page->index +1 , wpc, wbc, end_index); } - -/* -* Reserve log space if we might write beyond the on-disk inode size. -*/ - err =0 ; -if (ioend->io_type !=XFS_IO_UNWRITTEN &&xfs_ioend_is_append (ioend)) - err =xfs_setfilesize_trans_alloc (ioend); - -xfs_submit_ioend (wbc, iohead, err); -return 0 ; error: -if (iohead) -xfs_cancel_ioend (iohead); +/* +* We have to fail the iohead here because we buffers locked in the +* ioend chain. If we don't do this, we'll deadlock invalidating the +* page as that tries to lock the buffers on the page. Also, because we +* have set pages under writeback, we have to run IO completion to mark +* the error state of the IO appropriately, so we can't cancel the ioend +* directly here. That means we have to mark this page as under +* writeback if we included any buffers from it in the ioend chain. +*/ +if (count) +xfs_start_page_writeback (page,0 , count); +xfs_writepage_submit (wpc, wbc, err); -xfs_aops_discard_page (page); -ClearPageUptodate (page); -unlock_page (page); +/* +* We can only discard the page we had the IO error on if we haven't +* included it in the ioend above. If it has already been errored out, +* the it is unlocked and we can't touch it here. +*/ +if (!count) { +xfs_aops_discard_page (page); +ClearPageUptodate (page); +unlock_page (page); + } +mapping_set_error (page->mapping, err);return err; redirty:
@@ -1183,12 +1174,36 @@ redirty: } STATIC int +xfs_vm_writepage ( +struct page *page, +struct writeback_control *wbc) +{ +struct xfs_writepage_ctx wpc = { + .io_type =XFS_IO_OVERWRITE , + }; +int ret; + + ret =xfs_do_writepage (page, wbc, &wpc); +if (ret) +return ret; +return xfs_writepage_submit (&wpc, wbc, ret); +} + +STATIC intxfs_vm_writepages (struct address_space *mapping,struct writeback_control *wbc) { +struct xfs_writepage_ctx wpc = { + .io_type =XFS_IO_OVERWRITE , + }; +int ret; +xfs_iflags_clear (XFS_I (mapping->host),XFS_ITRUNCATED ); -return generic_writepages (mapping, wbc); + ret =write_cache_pages (mapping, wbc, xfs_do_writepage, &wpc); +if (ret) +return ret; +return xfs_writepage_submit (&wpc, wbc, ret); }/*
Signature · 6 lines
2.5.0 _______________________________________________ xfs mailing list [email protected] http://oss.sgi.com/mailman/listinfo/xfs
Re: [PATCH 2/4] xfs: Introduce writeback context for writepages
Quoted 13 lines · Dave Chinner
From: Dave Chinner <[email protected]>
xfs_vm_writepages()callsgeneric_writepagesto writeback a range of a file, but thenxfs_vm_writepage()clusters pages itself as it does not have any context it can passbetween->writepagecalls from__write_cache_pages().Introduce a writeback context for
xfs_vm_writepages()and call__write_cache_pagesdirectly with our own writepage callback so that we can pass that context to each writepage invocation. This encapsulates the current mapping, whether it is valid or not, the current ioend and it's IO type and the ioend chain being built.
Quoted 6 lines
This requires us to move the ioend submission up to the level where the writepage context is declared. This does mean we do not submit IO until we packaged the entire writeback range, but with the block plugging in the writepages call this is the way IO is submitted, anyway.
Ok, but the comment for blk_start_plug() mentions some kind of flush on task sleep mechanism. I could be wrong, but I take this to mean there are cases where I/O can initiate before the plug is stopped. Does deferring the I/O submission across writepages defeat that heuristic in any way? My (preliminary) understanding is that while the I/O submission would still be deferred by the plug in the same way in most cases, we're potentially holding back I/Os from the block infrastructure until the entire writepages sequence is complete.
Quoted 22 lines
It also means that we need to handle discontiguous page ranges. If the pages sent down by
write_cache_pagesto the writepage callback are discontiguous, we need to detect this and put each discontiguous page range into individual ioends. This is needed to ensure that the ioend accurately represents the range of the file that it covers so that file size updates during IO completion set the size correctly. Failure to take into account the discontiguous ranges results in files being too small when writeback patterns are non-sequential.Signed-off-by Dave Chinner <[email protected]>--- fs/xfs/xfs_aops.c | 277 ++++++++++++++++++++++++++++-------------------------- 1 file changed, 146 insertions(+), 131 deletions(-)fs/xfs/xfs_aops.c +0
-0@@ -36,6 +36,18 @@#include <linux/pagevec.h> #include <linux/writeback.h>
...
Quoted 26 lines
fs/xfs/xfs_aops.c +3
-14@@ -1151,29 +1135,36 @@ xfs_vm_writepage(if (end_index > last_index) end_index = last_index; -xfs_cluster_write (inode, page->index +1 , &imap, &ioend, - wbc, end_index); +xfs_cluster_write (inode, page->index +1 , wpc, wbc, end_index); } - -/* -* Reserve log space if we might write beyond the on-disk inode size. -*/ - err =0 ; -if (ioend->io_type !=XFS_IO_UNWRITTEN &&xfs_ioend_is_append (ioend)) - err =xfs_setfilesize_trans_alloc (ioend); - -xfs_submit_ioend (wbc, iohead, err); -return 0 ; error: -if (iohead) -xfs_cancel_ioend (iohead); +/* +* We have to fail the iohead here because we buffers locked in the
fs/xfs/xfs_aops.c xfs_vm_writepage( · line 1155
Quoted 10 lines
fs/xfs/xfs_aops.c +10
-0+* ioend chain. If we don't do this, we'll deadlock invalidating the +* page as that tries to lock the buffers on the page. Also, because we +* have set pages under writeback, we have to run IO completion to mark +* the error state of the IO appropriately, so we can't cancel the ioend +* directly here. That means we have to mark this page as under +* writeback if we included any buffers from it in the ioend chain. +*/ +if (count) +xfs_start_page_writeback (page,0 , count); +xfs_writepage_submit (wpc, wbc, err);
What are the error handling ramifications here for the previous, pending ioends? Previously, it looks like we would either fail in xfs_map_blocks() or submit I/O for each extent mapping. In other words, errors were not taken into consideration by the time we get into/past xfs_cluster_write().
Now it looks as though writepages carries on chaining ioends until we're done or hit an error, and then the entire ioend chain is subject to the error. I suppose a mapping error here is indicative of a larger problem, but do we really want to fail the entire writeback here? (If nothing else, the comments above should probably touch on this case).
Brian
Quoted 63 lines
fs/xfs/xfs_aops.c +36
-4-xfs_aops_discard_page (page); -ClearPageUptodate (page); -unlock_page (page); +/* +* We can only discard the page we had the IO error on if we haven't +* included it in the ioend above. If it has already been errored out, +* the it is unlocked and we can't touch it here. +*/ +if (!count) { +xfs_aops_discard_page (page); +ClearPageUptodate (page); +unlock_page (page); + } +mapping_set_error (page->mapping, err);return err; redirty:@@ -1183,12 +1174,36 @@ redirty: } STATIC int +xfs_vm_writepage ( +struct page *page, +struct writeback_control *wbc) +{ +struct xfs_writepage_ctx wpc = { + .io_type =XFS_IO_OVERWRITE , + }; +int ret; + + ret =xfs_do_writepage (page, wbc, &wpc); +if (ret) +return ret; +return xfs_writepage_submit (&wpc, wbc, ret); +} + +STATIC intxfs_vm_writepages (struct address_space *mapping,struct writeback_control *wbc) { +struct xfs_writepage_ctx wpc = { + .io_type =XFS_IO_OVERWRITE , + }; +int ret; +xfs_iflags_clear (XFS_I (mapping->host),XFS_ITRUNCATED ); -return generic_writepages (mapping, wbc); + ret =write_cache_pages (mapping, wbc, xfs_do_writepage, &wpc); +if (ret) +return ret; +return xfs_writepage_submit (&wpc, wbc, ret); }/* Signature · 6 lines
2.5.0 _______________________________________________ xfs mailing list [email protected] http://oss.sgi.com/mailman/listinfo/xfs
_______________________________________________
xfs mailing list
[email protected]
http://oss.sgi.com/mailman/listinfo/xfs
Re: [PATCH 2/4] xfs: Introduce writeback context for writepages
Quoted 8 lines · Brian Foster
Ok, but the comment for
blk_start_plug()mentions some kind of flush on task sleep mechanism. I could be wrong, but I take this to mean there are cases where I/O can initiate before the plug is stopped. Does deferring the I/O submission across writepages defeat that heuristic in any way? My (preliminary) understanding is that while the I/O submission would still be deferred by the plug in the same way in most cases, we're potentially holding back I/Os from the block infrastructure until the entire writepages sequence is complete.
Yes, we do. But the reason why the block layer needs to flush the plug on context switch is because we only have a limited bio mempool, and if processes that are not running consume that we can't make guaranteed progress. The XFS writeback code doesn't allocate bios until the end we are not affected by that particular issues, although we still need to worry about our own ioend mempools.
Sidenote: Jens now has the arbitrarily sized bio code in his queue for 4.3. With that we could replace our ioends with bios that have a little private data and simplify the submission phase of the writeback code significantly.
_______________________________________________
xfs mailing list
[email protected]
http://oss.sgi.com/mailman/listinfo/xfs
Re: [PATCH 2/4] xfs: Introduce writeback context for writepages
Quoted 10 lines · Christoph Hellwig
Quoted 8 lines · Brian Foster
Ok, but the comment for
blk_start_plug()mentions some kind of flush on task sleep mechanism. I could be wrong, but I take this to mean there are cases where I/O can initiate before the plug is stopped. Does deferring the I/O submission across writepages defeat that heuristic in any way? My (preliminary) understanding is that while the I/O submission would still be deferred by the plug in the same way in most cases, we're potentially holding back I/Os from the block infrastructure until the entire writepages sequence is complete.
Quoted 6 lines
Yes, we do. But the reason why the block layer needs to flush the plug on context switch is because we only have a limited bio mempool, and if processes that are not running consume that we can't make guaranteed progress. The XFS writeback code doesn't allocate bios until the end we are not affected by that particular issues, although we still need to worry about our own ioend mempools.
The patch changes the bio allocation patterns - it allocates them on the fly and holds them, so we could potentially exhaust the bio mempool with this submission technique. The ioend allocation pattern is different, too, because we only used to have 1 per buffer on a writepage call and the last one was used for the write clustering.
Quoted 4 lines
Sidenote: Jens now has the arbitrarily sized bio code in his queue for 4.3. With that we could replace our ioends with bios that have a little private data and simplify the submission phase of the writeback code significantly.
Yes, I've been keeping an eye on that and waiting for it to land as it solves many of the above problems. I still wanted to get the write cluster infrastructure changes underway, though, so I can work on making the writeback path not use bufferheads at all...
Cheers,
Dave.
Signature · 7 lines
Dave Chinner [email protected] _______________________________________________ xfs mailing list [email protected] http://oss.sgi.com/mailman/listinfo/xfs
Re: [PATCH 2/4] xfs: Introduce writeback context for writepages
Quoted 3 lines · Dave Chinner
The patch changes the bio allocation patterns - it allocates them on the fly and holds them, so we could potentially exhaust the bio mempool with this submission technique.
I've spend time to look over the patch again, and still don't see a change. Both in the old and new code we walk over the ioends and build bios on the fly in xfs_submit_ioend(), which is always called near then end of the writeback code; at the end of xfs_vm_writepage in the old version, and from the end of xfs_vm_writepage/xfs_vm_writepages through xfs_writepage_submit in the new code (not taking the error case into account, which probably should moe there, too).
The only big difference is..
Quoted 3 lines
The ioend allocation pattern
is different, too, because we only used to have 1 per buffer on a writepage call and the last one was used for the write clustering.
.. that we now build up way bigger ioend chains.
So back to Brians concern: we can now have fairly large piles of ioends built up while potentially getting scheduled out, and this does look like a potential real issue to me. I wonder if we should (ab-)use the blk_plug_cb infrastructure so that we can flush the pending ioends out on a context switch?
_______________________________________________
xfs mailing list
[email protected]
http://oss.sgi.com/mailman/listinfo/xfs
Re: [PATCH 2/4] xfs: Introduce writeback context for writepages
[ finally getting back to this :/ ]
Quoted 7 lines · Christoph Hellwig
Quoted 3 lines · Dave Chinner
The patch changes the bio allocation patterns - it allocates them on the fly and holds them, so we could potentially exhaust the bio mempool with this submission technique.
I've spend time to look over the patch again, and still don't see a change.
Ah, it's in the next patch that I haven't posted that "goes straight to bios". Ignore it for now...
Quoted 11 lines
Quoted 3 lines
The ioend allocation pattern
is different, too, because we only used to have 1 per buffer on a writepage call and the last one was used for the write clustering... that we now build up way bigger ioend chains.
So back to Brians concern: we can now have fairly large piles of ioends built up while potentially getting scheduled out, and this does look like a potential real issue to me. I wonder if we should (ab-)use the
blk_plug_cbinfrastructure so that we can flush the pending ioends out on a context switch?
Possibly, but I'm thinking that we should just end up building bios directly and submitting them once they are reach size limits of boundaries rather than building ioend chains for later submission.
Did the work for arbitrarily sized bios ever get merged? I can't find any evidence that it did....
Cheers,
Dave.
Signature · 7 lines
Dave Chinner [email protected] _______________________________________________ xfs mailing list [email protected] http://oss.sgi.com/mailman/listinfo/xfs
Re: [PATCH 2/4] xfs: Introduce writeback context for writepages
Quoted 2 lines · Dave Chinner
Did the work for arbitrarily sized bios ever get merged? I can't find any evidence that it did....
Yes, it landed in 4.3.
_______________________________________________
xfs mailing list
[email protected]
http://oss.sgi.com/mailman/listinfo/xfs
Re: [PATCH 2/4] xfs: Introduce writeback context for writepages
In reply to Dave ChinnerFYI, I recently started testing this series again after a trivial rebase to 4.5-rc2, and this patch seems to cause reproducible failures of generic/311 (fsync tester)
_______________________________________________
xfs mailing list
[email protected]
http://oss.sgi.com/mailman/listinfo/xfs
Re: [PATCH 2/4] xfs: Introduce writeback context for writepages
Quoted 3 lines · Christoph Hellwig
FYI, I recently started testing this series again after a trivial rebase to 4.5-rc2, and this patch seems to cause reproducible failures of generic/311 (fsync tester)
And by coincidence you posted a new version the night before I posted this mail. It still shows that same failure.
_______________________________________________
xfs mailing list
[email protected]
http://oss.sgi.com/mailman/listinfo/xfs
Re: [PATCH 2/4] xfs: Introduce writeback context for writepages
Quoted 7 lines · Christoph Hellwig
Quoted 3 lines · Christoph Hellwig
FYI, I recently started testing this series again after a trivial rebase to 4.5-rc2, and this patch seems to cause reproducible failures of generic/311 (fsync tester)
And by coincidence you posted a new version the night before I posted this mail. It still shows that same failure.
What is your test config? The only failures I've had recently of generic/311 were caused by a bug in the fsync-tester application. This was fixed by commit 9165a84 ("fsync-tester: reopen files with correct flags") that was pushed out in the fstests update I did yesterday.
Cheers,
Dave.
Signature · 7 lines
Dave Chinner [email protected] _______________________________________________ xfs mailing list [email protected] http://oss.sgi.com/mailman/listinfo/xfs
Re: [PATCH 2/4] xfs: Introduce writeback context for writepages
Quoted 5 lines · Dave Chinner
What is your test config? The only failures I've had recently of generic/311 were caused by a bug in the fsync-tester application. This was fixed by commit 9165a84 ("fsync-tester: reopen files with correct flags") that was pushed out in the fstests update I did yesterday.
Yeah, that seems to fix it.
_______________________________________________
xfs mailing list
[email protected]
http://oss.sgi.com/mailman/listinfo/xfs
PATCH v2 3/4 xfs: xfs_cluster_write is redundant
In reply to Dave ChinnerFrom: Dave Chinner <[email protected]>
xfs_cluster_write() is not necessary now that xfs_vm_writepages() aggregates writepage calls across a single mapping. This means we no longer need to do page lookups in xfs_cluster_write, so writeback only needs to look up th epage cache once per page being written. This also removes a large amount of mostly duplicate code between xfs_do_writepage() and xfs_convert_page().
--- fs/xfs/xfs_aops.c | 215 ++---------------------------------------------------- 1 file changed, 6 insertions(+), 209 deletions(-)
fs/xfs/xfs_aops.c +6 -209
@@ -644,179 +644,6 @@ xfs_check_page_type(return false; } -/* -* Allocate & map buffers for page given the extent map. Write it out. -* except for the original page of a writepage, this is called on -* delalloc/unwritten pages only, for the original page it is possible -* that the page has no mapping at all. -*/ -STATIC int -xfs_convert_page ( -struct inode *inode, -struct page *page, -loff_t tindex, -struct xfs_writepage_ctx *wpc, -struct writeback_control *wbc) -{ -struct buffer_head *bh, *head; -xfs_off_t end_offset; -unsigned long p_offset; -int len, page_dirty; -int count =0 , done =0 , uptodate =1 ; -xfs_off_t offset =page_offset (page); - -if (page->index != tindex) - goto fail; -if (!trylock_page (page)) - goto fail; -if (PageWriteback (page)) - goto fail_unlock_page; -if (page->mapping != inode->i_mapping) - goto fail_unlock_page; -if (!xfs_check_page_type (page, wpc->ioend->io_type, false)) - goto fail_unlock_page; - -/* -* page_dirty is initially a count of buffers on the page before -* EOF and is decremented as we move each into a cleanable state. -* -* Derivation: -* -* End offset is the highest offset that this page should represent. -* If we are on the last page, (end_offset & (PAGE_CACHE_SIZE - 1)) -* will evaluate non-zero and be less than PAGE_CACHE_SIZE and -* hence give us the correct page_dirty count. On any other page, -* it will be zero and in that case we need page_dirty to be the -* count of buffers on the page. -*/ - end_offset = min_t(unsigned long long, - (xfs_off_t)(page->index +1 ) <<PAGE_CACHE_SHIFT , -i_size_read (inode)); - -/* -* If the current map does not span the entire page we are about to try -* to write, then give up. The only way we can write a page that spans -* multiple mappings in a single writeback iteration is via the -* xfs_vm_writepage() function. Data integrity writeback requires the -* entire page to be written in a single attempt, otherwise the part of -* the page we don't write here doesn't get written as part of the data -* integrity sync. -* -* For normal writeback, we also don't attempt to write partial pages -* here as it simply means that write_cache_pages() will see it under -* writeback and ignore the page until some point in the future, at -* which time this will be the only page in the file that needs -* writeback. Hence for more optimal IO patterns, we should always -* avoid partial page writeback due to multiple mappings on a page here. -*/ -if (!xfs_imap_valid (inode, &wpc->imap, end_offset)) - goto fail_unlock_page; - - len =1 << inode->i_blkbits; - p_offset = min_t(unsigned long, end_offset & (PAGE_CACHE_SIZE - 1), -PAGE_CACHE_SIZE ); - p_offset = p_offset ?roundup (p_offset, len) :PAGE_CACHE_SIZE ; - page_dirty = p_offset / len; - -/* -* The moment we find a buffer that doesn't match our current type -* specification or can't be written, abort the loop and start -* writeback. As per the above xfs_imap_valid() check, only -* xfs_vm_writepage() can handle partial page writeback fully - we are -* limited here to the buffers that are contiguous with the current -* ioend, and hence a buffer we can't write breaks that contiguity and -* we have to defer the rest of the IO to xfs_vm_writepage(). -*/ - bh = head =page_buffers (page); -do { -if (offset >= end_offset) -break ; -if (!buffer_uptodate (bh)) - uptodate =0 ; -if (!(PageUptodate (page) ||buffer_uptodate (bh))) { - done =1 ; -break ; - } - -if (buffer_unwritten (bh) ||buffer_delay (bh) || -buffer_mapped (bh)) { -if (buffer_unwritten (bh)) - wpc->io_type =XFS_IO_UNWRITTEN ; -else if (buffer_delay (bh)) - wpc->io_type =XFS_IO_DELALLOC ; -else - wpc->io_type =XFS_IO_OVERWRITE ; - -/* -* imap should always be valid because of the above -* partial page end_offset check on the imap. -*/ -ASSERT (xfs_imap_valid (inode, &wpc->imap, offset)); - -lock_buffer (bh); -if (wpc->io_type !=XFS_IO_OVERWRITE ) -xfs_map_at_offset (inode, bh, &wpc->imap, offset); -xfs_add_to_ioend (inode, bh, offset, wpc); - - page_dirty--; - count++; - }else { - done =1 ; -break ; - } - }while (offset += len, (bh = bh->b_this_page) != head); - -if (uptodate && bh == head) -SetPageUptodate (page); - -if (count) { -if (--wbc->nr_to_write <=0 && - wbc->sync_mode ==WB_SYNC_NONE ) - done =1 ; - } -xfs_start_page_writeback (page, !page_dirty, count); - -return done; - fail_unlock_page: -unlock_page (page); - fail: -return 1 ; -} - -/* -* Convert & write out a cluster of pages in the same extent as defined -* by mp and following the start page. -*/ -STATIC void -xfs_cluster_write ( -struct inode *inode, -pgoff_t tindex, -struct xfs_writepage_ctx *wpc, -struct writeback_control *wbc, -pgoff_t tlast) -{ -struct pagevec pvec; -int done =0 , i; - -pagevec_init (&pvec,0 ); -while (!done && tindex <= tlast) { -unsigned len =min_t (pgoff_t,PAGEVEC_SIZE , tlast - tindex +1 ); - -if (!pagevec_lookup (&pvec, inode->i_mapping, tindex, len)) -break ; - -for (i =0 ; i <pagevec_count (&pvec); i++) { - done =xfs_convert_page (inode, pvec.pages[i], tindex++, - wpc, wbc); -if (done) -break ; - } - -pagevec_release (&pvec); -cond_resched (); - } -} - STATIC void xfs_vm_invalidatepage( struct page *page,
@@ -933,7 +760,7 @@ xfs_do_writepage(struct buffer_head *bh, *head;loff_t offset;__uint64_t end_offset; -pgoff_t end_index, last_index; +pgoff_t end_index;ssize_t len;int err, uptodate =1 ;int count =0 ;
@@ -963,12 +790,9 @@ xfs_do_writepage(if (WARN_ON_ONCE (current->flags &PF_FSTRANS )) goto redirty; -/* Is this page beyond the end of the file? */ - offset =i_size_read (inode); - end_index = offset >>PAGE_CACHE_SHIFT ; - last_index = (offset -1 ) >>PAGE_CACHE_SHIFT ; -/* +* Is this page beyond the end of the file? +* * The page index is less than the end_index, adjust the end_offset * to the highest offset that this page should represent. * -----------------------------------------------------
@@ -979,6 +803,8 @@ xfs_do_writepage(* | desired writeback range | see else | * ---------------------------------^------------------| */ + offset =i_size_read (inode); + end_index = offset >>PAGE_CACHE_SHIFT ;if (page->index < end_index) end_offset = (xfs_off_t)(page->index +1 ) <<PAGE_CACHE_SHIFT ;else {
@@ -1108,36 +934,7 @@ xfs_do_writepage(SetPageUptodate (page);xfs_start_page_writeback (page,1 , count); - -/* if there is no IO to be submitted for this page, we are done */ -if (!count) -return 0 ; - -ASSERT (wpc->iohead); - -/* -* Any errors from this point onwards need tobe reported through the IO -* completion path as we have marked the initial page as under writeback -* and unlocked it. -*/ -if (wpc->imap_valid) { -xfs_off_t end_index; - - end_index = wpc->imap.br_startoff + wpc->imap.br_blockcount; - -/* to bytes */ - end_index <<= inode->i_blkbits; - -/* to pages */ - end_index = (end_index -1 ) >>PAGE_CACHE_SHIFT ; - -/* check against file size */ -if (end_index > last_index) - end_index = last_index; - -xfs_cluster_write (inode, page->index +1 , wpc, wbc, end_index); - } - +ASSERT (wpc->iohead || !count);return 0 ; error:
Signature · 6 lines
2.5.0 _______________________________________________ xfs mailing list [email protected] http://oss.sgi.com/mailman/listinfo/xfs
PATCH v2 4/4 xfs: factor mapping out of xfs_do_writepage
In reply to Dave ChinnerFrom: Dave Chinner <[email protected]>
Separate out the bufferhead based mapping from the writepage code so that we have a clear separation of the page operations and the bufferhead state.
--- fs/xfs/xfs_aops.c | 221 +++++++++++++++++++++++++++++------------------------- 1 file changed, 119 insertions(+), 102 deletions(-)
fs/xfs/xfs_aops.c +119 -102
@@ -741,6 +741,116 @@ xfs_writepage_submit(return status; } +static int +xfs_writepage_map ( +struct xfs_writepage_ctx *wpc, +struct inode *inode, +struct page *page, +loff_t offset, +__uint64_t end_offset) +{ +struct buffer_head *bh, *head; +ssize_t len =1 << inode->i_blkbits; +int error =0 ; +int uptodate =1 ; +int count =0 ; + + bh = head =page_buffers (page); + offset =page_offset (page); + +do { +if (offset >= end_offset) +break ; +if (!buffer_uptodate (bh)) + uptodate =0 ; + +/* +* set_page_dirty dirties all buffers in a page, independent +* of their state. The dirty state however is entirely +* meaningless for holes (!mapped && uptodate), so skip +* buffers covering holes here. +*/ +if (!buffer_mapped (bh) &&buffer_uptodate (bh)) { + wpc->imap_valid = false; +continue ; + } + +if (buffer_unwritten (bh)) { +if (wpc->io_type !=XFS_IO_UNWRITTEN ) { + wpc->io_type =XFS_IO_UNWRITTEN ; + wpc->imap_valid = false; + } + }else if (buffer_delay (bh)) { +if (wpc->io_type !=XFS_IO_DELALLOC ) { + wpc->io_type =XFS_IO_DELALLOC ; + wpc->imap_valid = false; + } + }else if (buffer_uptodate (bh)) { +if (wpc->io_type !=XFS_IO_OVERWRITE ) { + wpc->io_type =XFS_IO_OVERWRITE ; + wpc->imap_valid = false; + } + }else { +if (PageUptodate (page)) +ASSERT (buffer_mapped (bh)); +/* +* This buffer is not uptodate and will not be +* written to disk. Ensure that we will put any +* subsequent writeable buffers into a new +* ioend. +*/ + wpc->imap_valid = false; +continue ; + } + +if (wpc->imap_valid) + wpc->imap_valid =xfs_imap_valid (inode, &wpc->imap, + offset); +if (!wpc->imap_valid) { + error =xfs_map_blocks (inode, offset, &wpc->imap, + wpc->io_type); +if (error) + goto out_error; + wpc->imap_valid =xfs_imap_valid (inode, &wpc->imap, + offset); + } +if (wpc->imap_valid) { +lock_buffer (bh); +if (wpc->io_type !=XFS_IO_OVERWRITE ) +xfs_map_at_offset (inode, bh, &wpc->imap, offset); +xfs_add_to_ioend (inode, bh, offset, wpc); + count++; + } + +if (!wpc->iohead) + wpc->iohead = wpc->ioend; + + }while (offset += len, ((bh = bh->b_this_page) != head)); + +if (uptodate && bh == head) +SetPageUptodate (page); + +xfs_start_page_writeback (page,1 , count); +ASSERT (wpc->iohead || !count); +return 0 ; + +out_error: +/* +* We can only discard the page we had the IO error on if we haven't +* included it in the ioend above. If it has already been added to the +* ioend, then we can't touch it here and need to rely on IO submission +* to unlock it. +*/ +if (count) +xfs_start_page_writeback (page,0 , count); +else { +xfs_aops_discard_page (page); +ClearPageUptodate (page); +unlock_page (page); + } +return error; +} +/* * Write out a dirty page. *
@@ -757,13 +867,10 @@ xfs_do_writepage( {struct xfs_writepage_ctx *wpc = data;struct inode *inode = page->mapping->host; -struct buffer_head *bh, *head;loff_t offset;__uint64_t end_offset;pgoff_t end_index; -ssize_t len; -int err, uptodate =1 ; -int count =0 ; +int error =0 ;trace_xfs_writepage (inode, page,0 ,0 );
@@ -856,113 +963,23 @@ xfs_do_writepage( end_offset = offset; } - len =1 << inode->i_blkbits; - - bh = head =page_buffers (page); - offset =page_offset (page); - -do { -if (offset >= end_offset) -break ; -if (!buffer_uptodate (bh)) - uptodate =0 ; - -/* -* set_page_dirty dirties all buffers in a page, independent -* of their state. The dirty state however is entirely -* meaningless for holes (!mapped && uptodate), so skip -* buffers covering holes here. -*/ -if (!buffer_mapped (bh) &&buffer_uptodate (bh)) { - wpc->imap_valid = false; -continue ; - } - -if (buffer_unwritten (bh)) { -if (wpc->io_type !=XFS_IO_UNWRITTEN ) { - wpc->io_type =XFS_IO_UNWRITTEN ; - wpc->imap_valid = false; - } - }else if (buffer_delay (bh)) { -if (wpc->io_type !=XFS_IO_DELALLOC ) { - wpc->io_type =XFS_IO_DELALLOC ; - wpc->imap_valid = false; - } - }else if (buffer_uptodate (bh)) { -if (wpc->io_type !=XFS_IO_OVERWRITE ) { - wpc->io_type =XFS_IO_OVERWRITE ; - wpc->imap_valid = false; - } - }else { -if (PageUptodate (page)) -ASSERT (buffer_mapped (bh)); -/* -* This buffer is not uptodate and will not be -* written to disk. Ensure that we will put any -* subsequent writeable buffers into a new -* ioend. -*/ - wpc->imap_valid = false; -continue ; - } - -if (wpc->imap_valid) - wpc->imap_valid =xfs_imap_valid (inode, &wpc->imap, - offset); -if (!wpc->imap_valid) { - err =xfs_map_blocks (inode, offset, &wpc->imap, - wpc->io_type); -if (err) - goto error; - wpc->imap_valid =xfs_imap_valid (inode, &wpc->imap, - offset); - } -if (wpc->imap_valid) { -lock_buffer (bh); -if (wpc->io_type !=XFS_IO_OVERWRITE ) -xfs_map_at_offset (inode, bh, &wpc->imap, offset); -xfs_add_to_ioend (inode, bh, offset, wpc); - count++; - } - -if (!wpc->iohead) - wpc->iohead = wpc->ioend; - - }while (offset += len, ((bh = bh->b_this_page) != head)); - -if (uptodate && bh == head) -SetPageUptodate (page); - -xfs_start_page_writeback (page,1 , count); -ASSERT (wpc->iohead || !count); + error =xfs_writepage_map (wpc, inode, page, offset, end_offset); +if (error) + goto out_error;return 0 ; -error: +out_error:/* * We have to fail the iohead here because we buffers locked in the * ioend chain. If we don't do this, we'll deadlock invalidating the * page as that tries to lock the buffers on the page. Also, because we * have set pages under writeback, we have to run IO completion to mark * the error state of the IO appropriately, so we can't cancel the ioend -* directly here. That means we have to mark this page as under -* writeback if we included any buffers from it in the ioend chain. +* directly here. */ -if (count) -xfs_start_page_writeback (page,0 , count); -xfs_writepage_submit (wpc, wbc, err); - -/* -* We can only discard the page we had the IO error on if we haven't -* included it in the ioend above. If it has already been errored out, -* the it is unlocked and we can't touch it here. -*/ -if (!count) { -xfs_aops_discard_page (page); -ClearPageUptodate (page); -unlock_page (page); - } -mapping_set_error (page->mapping, err); -return err; +xfs_writepage_submit (wpc, wbc, error); +mapping_set_error (page->mapping, error); +return error; redirty:redirty_page_for_writepage (wbc, page);
Signature · 6 lines
2.5.0 _______________________________________________ xfs mailing list [email protected] http://oss.sgi.com/mailman/listinfo/xfs