linux-kernel - [PATCH v5 02/18] mm/filemap: Remove dynamically allocated array from filemap

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Date:   Fri, 22 Jan 2021 16:01:24 +0000
From:   "Matthew Wilcox (Oracle)" <willy@...radead.org>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     "Matthew Wilcox (Oracle)" <willy@...radead.org>,
        linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Christoph Hellwig <hch@....de>,
        Miaohe Lin <linmiaohe@...wei.com>
Subject: [PATCH v5 02/18] mm/filemap: Remove dynamically allocated array from filemap_read

Increasing the batch size runs into diminishing returns.  It's probably
better to make, eg, three calls to filemap_get_pages() than it is to
call into kmalloc().

Signed-off-by: Matthew Wilcox (Oracle) <willy@...radead.org>
Reviewed-by: Christoph Hellwig <hch@....de>
Reviewed-by: Miaohe Lin <linmiaohe@...wei.com>
---
 mm/filemap.c | 15 ++-------------
 1 file changed, 2 insertions(+), 13 deletions(-)

diff --git a/mm/filemap.c b/mm/filemap.c
index afc0f674f2242..a5c4f7ddfc40c 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2444,8 +2444,8 @@ ssize_t generic_file_buffered_read(struct kiocb *iocb,
 	struct file_ra_state *ra = &filp->f_ra;
 	struct address_space *mapping = filp->f_mapping;
 	struct inode *inode = mapping->host;
-	struct page *pages_onstack[PAGEVEC_SIZE], **pages = NULL;
-	unsigned int nr_pages = min_t(unsigned int, 512,
+	struct page *pages[PAGEVEC_SIZE];
+	unsigned int nr_pages = min_t(unsigned int, PAGEVEC_SIZE,
 			((iocb->ki_pos + iter->count + PAGE_SIZE - 1) >> PAGE_SHIFT) -
 			(iocb->ki_pos >> PAGE_SHIFT));
 	int i, pg_nr, error = 0;
@@ -2459,14 +2459,6 @@ ssize_t generic_file_buffered_read(struct kiocb *iocb,
 
 	iov_iter_truncate(iter, inode->i_sb->s_maxbytes);
 
-	if (nr_pages > ARRAY_SIZE(pages_onstack))
-		pages = kmalloc_array(nr_pages, sizeof(void *), GFP_KERNEL);
-
-	if (!pages) {
-		pages = pages_onstack;
-		nr_pages = min_t(unsigned int, nr_pages, ARRAY_SIZE(pages_onstack));
-	}
-
 	do {
 		cond_resched();
 
@@ -2551,9 +2543,6 @@ ssize_t generic_file_buffered_read(struct kiocb *iocb,
 
 	file_accessed(filp);
 
-	if (pages != pages_onstack)
-		kfree(pages);
-
 	return written ? written : error;
 }
 EXPORT_SYMBOL_GPL(generic_file_buffered_read);
-- 
2.29.2