All of lore.kernel.org
 help / color / mirror / Atom feed
From: Jens Axboe <axboe@kernel.dk>
To: linux-fsdevel@vger.kernel.org, linux-mm@kvack.org
Cc: hch@infradead.org, akpm@linux-foundation.org,
	Jens Axboe <axboe@kernel.dk>
Subject: [PATCH 1/3] mm: provide filemap_range_needs_writeback() helper
Date: Mon,  8 Feb 2021 19:30:06 -0700	[thread overview]
Message-ID: <20210209023008.76263-2-axboe@kernel.dk> (raw)
In-Reply-To: <20210209023008.76263-1-axboe@kernel.dk>

For O_DIRECT reads/writes, we check if we need to issue a call to
filemap_write_and_wait_range() to issue and/or wait for writeback for any
page in the given range. The existing mechanism just checks for a page in
the range, which is suboptimal for IOCB_NOWAIT as we'll fallback to the
slow path (and needing retry) if there's just a clean page cache page in
the range.

Provide filemap_range_needs_writeback() which tries a little harder to
check if we actually need to issue and/or wait for writeback in the
range.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 include/linux/fs.h |  2 ++
 mm/filemap.c       | 43 +++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 45 insertions(+)

diff --git a/include/linux/fs.h b/include/linux/fs.h
index fd47deea7c17..def89222dfe9 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2633,6 +2633,8 @@ static inline int filemap_fdatawait(struct address_space *mapping)
 
 extern bool filemap_range_has_page(struct address_space *, loff_t lstart,
 				  loff_t lend);
+extern bool filemap_range_needs_writeback(struct address_space *,
+					  loff_t lstart, loff_t lend);
 extern int filemap_write_and_wait_range(struct address_space *mapping,
 				        loff_t lstart, loff_t lend);
 extern int __filemap_fdatawrite_range(struct address_space *mapping,
diff --git a/mm/filemap.c b/mm/filemap.c
index aa0e0fb04670..6a58d50fbd31 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -633,6 +633,49 @@ static bool mapping_needs_writeback(struct address_space *mapping)
 	return mapping->nrpages;
 }
 
+/**
+ * filemap_range_needs_writeback - check if range potentially needs writeback
+ * @mapping:           address space within which to check
+ * @start_byte:        offset in bytes where the range starts
+ * @end_byte:          offset in bytes where the range ends (inclusive)
+ *
+ * Find at least one page in the range supplied, usually used to check if
+ * direct writing in this range will trigger a writeback. Used by O_DIRECT
+ * read/write with IOCB_NOWAIT, to see if the caller needs to do
+ * filemap_write_and_wait_range() before proceeding.
+ *
+ * Return: %true if the caller should do filemap_write_and_wait_range() before
+ * doing O_DIRECT to a page in this range, %false otherwise.
+ */
+bool filemap_range_needs_writeback(struct address_space *mapping,
+				   loff_t start_byte, loff_t end_byte)
+{
+	XA_STATE(xas, &mapping->i_pages, start_byte >> PAGE_SHIFT);
+	pgoff_t max = end_byte >> PAGE_SHIFT;
+	struct page *page;
+
+	if (!mapping_needs_writeback(mapping))
+		return false;
+	if (!mapping_tagged(mapping, PAGECACHE_TAG_DIRTY) &&
+	    !mapping_tagged(mapping, PAGECACHE_TAG_WRITEBACK))
+		return false;
+	if (end_byte < start_byte)
+		return false;
+
+	rcu_read_lock();
+	xas_for_each(&xas, page, max) {
+		if (xas_retry(&xas, page))
+			continue;
+		if (xa_is_value(page))
+			continue;
+		if (PageDirty(page) || PageLocked(page) || PageWriteback(page))
+			break;
+	}
+	rcu_read_unlock();
+	return page != NULL;
+}
+EXPORT_SYMBOL_GPL(filemap_range_needs_writeback);
+
 /**
  * filemap_write_and_wait_range - write out & wait on a file range
  * @mapping:	the address_space for the pages
-- 
2.30.0


  reply	other threads:[~2021-02-09  2:31 UTC|newest]

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-02-09  2:30 [PATCHSET v2 0/3] Improve IOCB_NOWAIT O_DIRECT reads Jens Axboe
2021-02-09  2:30 ` Jens Axboe [this message]
2021-02-09  7:47   ` [PATCH 1/3] mm: provide filemap_range_needs_writeback() helper Christoph Hellwig
2021-02-09 14:30     ` Jens Axboe
2021-02-09  2:30 ` [PATCH 2/3] mm: use filemap_range_needs_writeback() for O_DIRECT reads Jens Axboe
2021-02-09  7:48   ` Christoph Hellwig
2021-02-09 14:27     ` Jens Axboe
2021-02-09  2:30 ` [PATCH 3/3] iomap: " Jens Axboe
2021-02-09  7:51   ` Christoph Hellwig
2021-02-09 14:29     ` Jens Axboe
2021-02-09 19:55 ` [PATCHSET v2 0/3] Improve IOCB_NOWAIT " Andrew Morton
2021-02-09 20:11   ` Jens Axboe
2021-02-10  8:07     ` Sedat Dilek
2021-02-10  8:07       ` Sedat Dilek
2021-02-10 14:47       ` Jens Axboe
  -- strict thread matches above, loose matches on Subject: below --
2021-02-24 16:44 [PATCHSET v3 " Jens Axboe
2021-02-24 16:44 ` [PATCH 1/3] mm: provide filemap_range_needs_writeback() helper Jens Axboe
2021-02-24 16:50   ` Matthew Wilcox
2021-02-24 16:53     ` Jens Axboe
2021-02-24 17:22   ` Jan Kara
2021-02-08 22:18 [PATCHSET 0/3] Improve IOCB_NOWAIT O_DIRECT Jens Axboe
2021-02-08 22:18 ` [PATCH 1/3] mm: provide filemap_range_needs_writeback() helper Jens Axboe
2021-02-08 23:02   ` Matthew Wilcox
2021-02-08 23:21     ` Jens Axboe

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20210209023008.76263-2-axboe@kernel.dk \
    --to=axboe@kernel.dk \
    --cc=akpm@linux-foundation.org \
    --cc=hch@infradead.org \
    --cc=linux-fsdevel@vger.kernel.org \
    --cc=linux-mm@kvack.org \
    --subject='Re: [PATCH 1/3] mm: provide filemap_range_needs_writeback() helper' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.