linux-kernel - [PATCH] drm/i915: Stop reconfiguring our shmemfs mountpoint

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Date:   Thu,  8 Aug 2019 18:22:26 +0100
From:   Chris Wilson <chris@...is-wilson.co.uk>
To:     intel-gfx@...ts.freedesktop.org
Cc:     linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        Chris Wilson <chris@...is-wilson.co.uk>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Sedat Dilek <sedat.dilek@...il.com>,
        Hugh Dickins <hughd@...gle.com>,
        Matthew Auld <matthew.auld@...el.com>,
        Al Viro <viro@...iv.linux.org.uk>
Subject: [PATCH] drm/i915: Stop reconfiguring our shmemfs mountpoint

The filesystem reconfigure API is undergoing a transition, breaking our
current code. As we only set the default options, we can simply remove
the call to s_op->remount_fs(). In the future, when HW permits, we can
try re-enabling huge page support, albeit as suggested with new per-file
controls.

Reported-by: Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Reported-by: Sedat Dilek <sedat.dilek@...il.com>
Suggested-by: Hugh Dickins <hughd@...gle.com>
Signed-off-by: Chris Wilson <chris@...is-wilson.co.uk>
Cc: Matthew Auld <matthew.auld@...el.com>
Cc: Hugh Dickins <hughd@...gle.com>
Cc: Al Viro <viro@...iv.linux.org.uk>
Cc: Sergey Senozhatsky <sergey.senozhatsky@...il.com>
---
 drivers/gpu/drm/i915/gem/i915_gemfs.c | 31 ++++++++-------------------
 1 file changed, 9 insertions(+), 22 deletions(-)

diff --git a/drivers/gpu/drm/i915/gem/i915_gemfs.c b/drivers/gpu/drm/i915/gem/i915_gemfs.c
index 099f3397aada..be94598cb304 100644
--- a/drivers/gpu/drm/i915/gem/i915_gemfs.c
+++ b/drivers/gpu/drm/i915/gem/i915_gemfs.c
@@ -20,31 +20,18 @@ int i915_gemfs_init(struct drm_i915_private *i915)
 	if (!type)
 		return -ENODEV;
 
-	gemfs = kern_mount(type);
-	if (IS_ERR(gemfs))
-		return PTR_ERR(gemfs);
-
 	/*
-	 * Enable huge-pages for objects that are at least HPAGE_PMD_SIZE, most
-	 * likely 2M. Note that within_size may overallocate huge-pages, if say
-	 * we allocate an object of size 2M + 4K, we may get 2M + 2M, but under
-	 * memory pressure shmem should split any huge-pages which can be
-	 * shrunk.
+	 * By creating our own shmemfs mountpoint, we can pass in
+	 * mount flags that better match our usecase.
+	 *
+	 * One example, although it is probably better with a per-file
+	 * control, is selecting huge page allocations ("huge=within").
+	 * Currently unused due to bandwidth issues (slow reads) on Broadwell+.
 	 */
 
-	if (has_transparent_hugepage()) {
-		struct super_block *sb = gemfs->mnt_sb;
-		/* FIXME: Disabled until we get W/A for read BW issue. */
-		char options[] = "huge=never";
-		int flags = 0;
-		int err;
-
-		err = sb->s_op->remount_fs(sb, &flags, options);
-		if (err) {
-			kern_unmount(gemfs);
-			return err;
-		}
-	}
+	gemfs = kern_mount(type);
+	if (IS_ERR(gemfs))
+		return PTR_ERR(gemfs);
 
 	i915->mm.gemfs = gemfs;
 
-- 
2.23.0.rc1