linux-kernel - [PATCH] mm : update ra->ra_pages if it's NOT equal to bdi->ra

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Date:   Fri, 14 Aug 2020 09:30:11 +0800
From:   Zhaoyang Huang <huangzhaoyang@...il.com>
To:     Roman Gushchin <klamm@...dex-team.ru>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Zhaoyang Huang <zhaoyang.huang@...soc.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH] mm : update ra->ra_pages if it's NOT equal to bdi->ra_pages

file->f_ra->ra_pages will remain the initialized value since it opend, which may
be NOT equal to bdi->ra_pages as the latter one is updated somehow(etc,
echo xxx > /sys/block/dm/queue/read_ahead_kb).So sync ra->ra_pages to the
updated value when sync read.

Signed-off-by: Zhaoyang Huang <zhaoyang.huang@...soc.com>
---
 mm/filemap.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/mm/filemap.c b/mm/filemap.c
index d78f577..5c2d7cc 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2470,6 +2470,8 @@ static struct file *do_sync_mmap_readahead(struct vm_fault *vmf)
 	struct file *fpin = NULL;
 	pgoff_t offset = vmf->pgoff;
 
+	if (ra->ra_pages != inode_to_bdi(mapping->host)->ra_pages)
+		ra->ra_pages = inode_to_bdi(mapping->host)->ra_pages;
 	/* If we don't want any read-ahead, don't bother */
 	if (vmf->vma->vm_flags & VM_RAND_READ)
 		return fpin;
-- 
1.9.1