linux-kernel - Re: [PATCH v12 00/10] enable bs

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Message-ID: <3452631.1724080629@warthog.procyon.org.uk>
Date: Mon, 19 Aug 2024 16:17:09 +0100
From: David Howells <dhowells@...hat.com>
To: "Pankaj Raghav (Samsung)" <kernel@...kajraghav.com>
Cc: dhowells@...hat.com, brauner@...nel.org, akpm@...ux-foundation.org,
    chandan.babu@...cle.com, linux-fsdevel@...r.kernel.org,
    djwong@...nel.org, hare@...e.de, gost.dev@...sung.com,
    linux-xfs@...r.kernel.org, hch@....de, david@...morbit.com,
    Zi Yan <ziy@...dia.com>, yang@...amperecomputing.com,
    linux-kernel@...r.kernel.org, linux-mm@...ck.org,
    willy@...radead.org, john.g.garry@...cle.com,
    cl@...amperecomputing.com, p.raghav@...sung.com, mcgrof@...nel.org,
    ryan.roberts@....com
Subject: Re: [PATCH v12 00/10] enable bs > ps in XFS

Okay, the code in netfs_invalidate_folio() isn't correct in the way it reduces
streaming writes.  Attached is a patch that shows some of the changes I need
to make - but this is not yet working.

David
---
diff --git a/fs/netfs/misc.c b/fs/netfs/misc.c
index eaa0a992d178..e237c771eeb5 100644
--- a/fs/netfs/misc.c
+++ b/fs/netfs/misc.c
@@ -214,18 +215,34 @@ void netfs_invalidate_folio(struct folio *folio, size_t offset, size_t length)
 		/* We have a partially uptodate page from a streaming write. */
 		unsigned int fstart = finfo->dirty_offset;
 		unsigned int fend = fstart + finfo->dirty_len;
-		unsigned int end = offset + length;
+		unsigned int iend = offset + length;
 
 		if (offset >= fend)
 			return;
-		if (end <= fstart)
+		if (iend <= fstart)
+			return;
+
+		/* The invalidation region overlaps the data.  If the region
+		 * covers the start of the data, we either move along the start
+		 * or just erase the data entirely.
+		 */
+		if (offset <= fstart) {
+			if (iend >= fend)
+				goto erase_completely;
+			/* Move the start of the data. */
+			finfo->dirty_len = fend - iend;
+			finfo->dirty_offset = offset;
 			return;
-		if (offset <= fstart && end >= fend)
-			goto erase_completely;
-		if (offset <= fstart && end > fstart)
-			goto reduce_len;
-		if (offset > fstart && end >= fend)
-			goto move_start;
+		}
+
+		/* Reduce the length of the data if the invalidation region
+		 * covers the tail part.
+		 */
+		if (iend >= fend) {
+			finfo->dirty_len = offset - fstart;
+			return;
+		}
+
 		/* A partial write was split.  The caller has already zeroed
 		 * it, so just absorb the hole.
 		 */
@@ -238,12 +261,6 @@ void netfs_invalidate_folio(struct folio *folio, size_t offset, size_t length)
 	folio_clear_uptodate(folio);
 	kfree(finfo);
 	return;
-reduce_len:
-	finfo->dirty_len = offset + length - finfo->dirty_offset;
-	return;
-move_start:
-	finfo->dirty_len -= offset - finfo->dirty_offset;
-	finfo->dirty_offset = offset;
 }
 EXPORT_SYMBOL(netfs_invalidate_folio);