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Subject[patch 21/27] combine generic_writepages() and mpage_writepages()


generic_writepages and mpage_writepages are basically identical,
except one calls ->writepage() and the other calls mpage_writepage().
This duplication is irritating.

The patch folds generic_writepage() into mpage_writepages(). It does
this rather kludgily: if the get_block argument to mpage_writepages()
is NULL then use ->writepage().

Can't think of a better way, really - we could go for a fully-blown
write_actor_t thing, but that would be overly elaborate and would not
allow mpage_writepage() to be inlined inside mpage_writepages(), which
is rather desirable.




fs/mpage.c | 55 +++++++++++++++++++++++++--
mm/page-writeback.c | 104 +---------------------------------------------------
2 files changed, 53 insertions(+), 106 deletions(-)
--- 2.5.24/mm/page-writeback.c~consolidate-writepages Thu Jul 4 16:17:30 2002
+++ 2.5.24-akpm/mm/page-writeback.c Thu Jul 4 16:17:30 2002
@@ -19,8 +19,9 @@
#include <linux/pagemap.h>
#include <linux/writeback.h>
#include <linux/init.h>
-#include <linux/sysrq.h>
+//#include <linux/sysrq.h>
#include <linux/backing-dev.h>
+#include <linux/mpage.h>

/*
* The maximum number of pages to writeout in a single bdflush/kupdate
@@ -313,108 +314,9 @@ int generic_vm_writeback(struct page *pa
}
EXPORT_SYMBOL(generic_vm_writeback);

-/**
- * generic_writepages - walk the list of dirty pages of the given
- * address space and writepage() all of them.
- *
- * @mapping: address space structure to write
- * @nr_to_write: subtract the number of written pages from *@nr_to_write
- *
- * This is a library function, which implements the writepages()
- * address_space_operation.
- *
- * (The next two paragraphs refer to code which isn't here yet, but they
- * explain the presence of address_space.io_pages)
- *
- * Pages can be moved from clean_pages or locked_pages onto dirty_pages
- * at any time - it's not possible to lock against that. So pages which
- * have already been added to a BIO may magically reappear on the dirty_pages
- * list. And generic_writepages() will again try to lock those pages.
- * But I/O has not yet been started against the page. Thus deadlock.
- *
- * To avoid this, the entire contents of the dirty_pages list are moved
- * onto io_pages up-front. We then walk io_pages, locking the
- * pages and submitting them for I/O, moving them to locked_pages.
- *
- * This has the added benefit of preventing a livelock which would otherwise
- * occur if pages are being dirtied faster than we can write them out.
- *
- * If a page is already under I/O, generic_writepages() skips it, even
- * if it's dirty. This is desirable behaviour for memory-cleaning writeback,
- * but it is INCORRECT for data-integrity system calls such as fsync(). fsync()
- * and msync() need to guarentee that all the data which was dirty at the time
- * the call was made get new I/O started against them. The way to do this is
- * to run filemap_fdatawait() before calling filemap_fdatawrite().
- *
- * It's fairly rare for PageWriteback pages to be on ->dirty_pages. It
- * means that someone redirtied the page while it was under I/O.
- */
int generic_writepages(struct address_space *mapping, int *nr_to_write)
{
- int (*writepage)(struct page *) = mapping->a_ops->writepage;
- int ret = 0;
- int done = 0;
- int err;
-
- write_lock(&mapping->page_lock);
-
- list_splice(&mapping->dirty_pages, &mapping->io_pages);
- INIT_LIST_HEAD(&mapping->dirty_pages);
-
- while (!list_empty(&mapping->io_pages) && !done) {
- struct page *page = list_entry(mapping->io_pages.prev,
- struct page, list);
- list_del(&page->list);
- if (PageWriteback(page)) {
- if (PageDirty(page)) {
- list_add(&page->list, &mapping->dirty_pages);
- continue;
- }
- list_add(&page->list, &mapping->locked_pages);
- continue;
- }
- if (!PageDirty(page)) {
- list_add(&page->list, &mapping->clean_pages);
- continue;
- }
- list_add(&page->list, &mapping->locked_pages);
- page_cache_get(page);
- write_unlock(&mapping->page_lock);
- lock_page(page);
-
- /* It may have been removed from swapcache: check ->mapping */
- if (page->mapping && !PageWriteback(page) &&
- TestClearPageDirty(page)) {
- /* FIXME: batch this up */
- if (!PageActive(page) && PageLRU(page)) {
- spin_lock(&pagemap_lru_lock);
- if (!PageActive(page) && PageLRU(page)) {
- list_del(&page->lru);
- list_add(&page->lru, &inactive_list);
- }
- spin_unlock(&pagemap_lru_lock);
- }
- err = writepage(page);
- if (!ret)
- ret = err;
- if (nr_to_write && --(*nr_to_write) <= 0)
- done = 1;
- } else {
- unlock_page(page);
- }
-
- page_cache_release(page);
- write_lock(&mapping->page_lock);
- }
- if (!list_empty(&mapping->io_pages)) {
- /*
- * Put the rest back, in the correct order.
- */
- list_splice(&mapping->io_pages, mapping->dirty_pages.prev);
- INIT_LIST_HEAD(&mapping->io_pages);
- }
- write_unlock(&mapping->page_lock);
- return ret;
+ return mpage_writepages(mapping, nr_to_write, NULL);
}
EXPORT_SYMBOL(generic_writepages);

--- 2.5.24/fs/mpage.c~consolidate-writepages Thu Jul 4 16:17:30 2002
+++ 2.5.24-akpm/fs/mpage.c Thu Jul 4 16:17:30 2002
@@ -475,9 +475,44 @@ out:
return bio;
}

-/*
- * This is a cut-n-paste of generic_writepages(). We _could_
- * generalise that function. It'd get a bit messy. We'll see.
+/**
+ * mpage_writepages - walk the list of dirty pages of the given
+ * address space and writepage() all of them.
+ *
+ * @mapping: address space structure to write
+ * @nr_to_write: subtract the number of written pages from *@nr_to_write
+ * @get_block: the filesystem's block mapper function.
+ * If this is NULL then use a_ops->writepage. Otherwise, go
+ * direct-to-BIO.
+ *
+ * This is a library function, which implements the writepages()
+ * address_space_operation.
+ *
+ * (The next two paragraphs refer to code which isn't here yet, but they
+ * explain the presence of address_space.io_pages)
+ *
+ * Pages can be moved from clean_pages or locked_pages onto dirty_pages
+ * at any time - it's not possible to lock against that. So pages which
+ * have already been added to a BIO may magically reappear on the dirty_pages
+ * list. And generic_writepages() will again try to lock those pages.
+ * But I/O has not yet been started against the page. Thus deadlock.
+ *
+ * To avoid this, the entire contents of the dirty_pages list are moved
+ * onto io_pages up-front. We then walk io_pages, locking the
+ * pages and submitting them for I/O, moving them to locked_pages.
+ *
+ * This has the added benefit of preventing a livelock which would otherwise
+ * occur if pages are being dirtied faster than we can write them out.
+ *
+ * If a page is already under I/O, generic_writepages() skips it, even
+ * if it's dirty. This is desirable behaviour for memory-cleaning writeback,
+ * but it is INCORRECT for data-integrity system calls such as fsync(). fsync()
+ * and msync() need to guarentee that all the data which was dirty at the time
+ * the call was made get new I/O started against them. The way to do this is
+ * to run filemap_fdatawait() before calling filemap_fdatawrite().
+ *
+ * It's fairly rare for PageWriteback pages to be on ->dirty_pages. It
+ * means that someone redirtied the page while it was under I/O.
*/
int
mpage_writepages(struct address_space *mapping,
@@ -487,6 +522,11 @@ mpage_writepages(struct address_space *m
sector_t last_block_in_bio = 0;
int ret = 0;
int done = 0;
+ int (*writepage)(struct page *);
+
+ writepage = NULL;
+ if (get_block == NULL)
+ writepage = mapping->a_ops->writepage;

write_lock(&mapping->page_lock);

@@ -526,8 +566,13 @@ mpage_writepages(struct address_space *m
}
spin_unlock(&pagemap_lru_lock);
}
- bio = mpage_writepage(bio, page, get_block,
- &last_block_in_bio, &ret);
+
+ if (writepage) {
+ ret = (*writepage)(page);
+ } else {
+ bio = mpage_writepage(bio, page, get_block,
+ &last_block_in_bio, &ret);
+ }
if (ret || (nr_to_write && --(*nr_to_write) <= 0))
done = 1;
} else {
-
-
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