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().

Link: https://lkml.kernel.org/r/20210122160140.223228-3-willy@infradead.org
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Miaohe Lin <linmiaohe@huawei.com>
Cc: Kent Overstreet <kent.overstreet@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/filemap.c b/mm/filemap.c
index fbfea44..f621a7d 100644 (file)
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2431,8 +2431,8 @@ 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;
@@ -2446,14 +2446,6 @@ 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();
 
@@ -2538,9 +2530,6 @@ put_pages:
 
        file_accessed(filp);
 
-       if (pages != pages_onstack)
-               kfree(pages);
-
        return written ? written : error;
 }
 EXPORT_SYMBOL_GPL(generic_file_buffered_read);