Commit 0c7c575d authored by Matthew Wilcox (Oracle)'s avatar Matthew Wilcox (Oracle) Committed by Linus Torvalds
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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: default avatarMatthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: default avatarChristoph Hellwig <hch@lst.de>
Reviewed-by: default avatarMiaohe Lin <linmiaohe@huawei.com>
Cc: Kent Overstreet <kent.overstreet@gmail.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 3a6bae48

mm/filemap.c

+2 −13
Original line number Diff line number Diff line
@@ -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 @@ 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);