From: "Matthew Wilcox (Oracle)" <willy@xxxxxxxxxxxxx> Subject: 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@xxxxxxxxxxxxx Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx> Reviewed-by: Christoph Hellwig <hch@xxxxxx> Reviewed-by: Miaohe Lin <linmiaohe@xxxxxxxxxx> Cc: Kent Overstreet <kent.overstreet@xxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/filemap.c | 15 ++------------- 1 file changed, 2 insertions(+), 13 deletions(-) --- a/mm/filemap.c~mm-filemap-remove-dynamically-allocated-array-from-filemap_read +++ a/mm/filemap.c @@ -2431,8 +2431,8 @@ ssize_t generic_file_buffered_read(struc 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(struc 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); _
