From: "Matthew Wilcox (Oracle)" <willy@xxxxxxxxxxxxx> Subject: mm/filemap: use head pages in generic_file_buffered_read Add filemap_get_read_batch() which returns the head pages which represent a contiguous array of bytes in the file. It also stops when encountering a page marked as Readahead or !Uptodate (but does return that page) so it can be handled appropriately by filemap_get_pages(). That lets us remove the loop in filemap_get_pages() and check only the last page. Link: https://lkml.kernel.org/r/20210122160140.223228-5-willy@xxxxxxxxxxxxx Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx> Reviewed-by: Kent Overstreet <kent.overstreet@xxxxxxxxx> Reviewed-by: Christoph Hellwig <hch@xxxxxx> Cc: Miaohe Lin <linmiaohe@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/filemap.c | 122 ++++++++++++++++++++++++++++++++++--------------- 1 file changed, 85 insertions(+), 37 deletions(-) --- a/mm/filemap.c~mm-filemap-use-head-pages-in-generic_file_buffered_read +++ a/mm/filemap.c @@ -2178,6 +2178,51 @@ static int lock_page_for_iocb(struct kio return lock_page_killable(page); } +/* + * filemap_get_read_batch - Get a batch of pages for read + * + * Get a batch of pages which represent a contiguous range of bytes + * in the file. No tail pages will be returned. If @index is in the + * middle of a THP, the entire THP will be returned. The last page in + * the batch may have Readahead set or be not Uptodate so that the + * caller can take the appropriate action. + */ +static void filemap_get_read_batch(struct address_space *mapping, + pgoff_t index, pgoff_t max, struct pagevec *pvec) +{ + XA_STATE(xas, &mapping->i_pages, index); + struct page *head; + + rcu_read_lock(); + for (head = xas_load(&xas); head; head = xas_next(&xas)) { + if (xas_retry(&xas, head)) + continue; + if (xas.xa_index > max || xa_is_value(head)) + break; + if (!page_cache_get_speculative(head)) + goto retry; + + /* Has the page moved or been split? */ + if (unlikely(head != xas_reload(&xas))) + goto put_page; + + if (!pagevec_add(pvec, head)) + break; + if (!PageUptodate(head)) + break; + if (PageReadahead(head)) + break; + xas.xa_index = head->index + thp_nr_pages(head) - 1; + xas.xa_offset = (xas.xa_index >> xas.xa_shift) & XA_CHUNK_MASK; + continue; +put_page: + put_page(head); +retry: + xas_reset(&xas); + } + rcu_read_unlock(); +} + static struct page *filemap_read_page(struct kiocb *iocb, struct file *filp, struct address_space *mapping, struct page *page) { @@ -2331,15 +2376,15 @@ static int filemap_get_pages(struct kioc struct address_space *mapping = filp->f_mapping; struct file_ra_state *ra = &filp->f_ra; pgoff_t index = iocb->ki_pos >> PAGE_SHIFT; - pgoff_t last_index = (iocb->ki_pos + iter->count + PAGE_SIZE-1) >> PAGE_SHIFT; - unsigned int nr = min_t(unsigned long, last_index - index, PAGEVEC_SIZE); - int i, j, err = 0; + pgoff_t last_index; + int err = 0; + last_index = DIV_ROUND_UP(iocb->ki_pos + iter->count, PAGE_SIZE); find_page: if (fatal_signal_pending(current)) return -EINTR; - pvec->nr = find_get_pages_contig(mapping, index, nr, pvec->pages); + filemap_get_read_batch(mapping, index, last_index, pvec); if (pvec->nr) goto got_pages; @@ -2348,29 +2393,30 @@ find_page: page_cache_sync_readahead(mapping, ra, filp, index, last_index - index); - pvec->nr = find_get_pages_contig(mapping, index, nr, pvec->pages); + filemap_get_read_batch(mapping, index, last_index, pvec); if (pvec->nr) goto got_pages; pvec->pages[0] = filemap_create_page(iocb, iter); err = PTR_ERR_OR_ZERO(pvec->pages[0]); - if (!IS_ERR_OR_NULL(pvec->pages[0])) - pvec->nr = 1; + if (IS_ERR_OR_NULL(pvec->pages[0])) + goto err; + pvec->nr = 1; + return 0; got_pages: - for (i = 0; i < pvec->nr; i++) { - struct page *page = pvec->pages[i]; - pgoff_t pg_index = index + i; + { + struct page *page = pvec->pages[pvec->nr - 1]; + pgoff_t pg_index = page->index; loff_t pg_pos = max(iocb->ki_pos, (loff_t) pg_index << PAGE_SHIFT); loff_t pg_count = iocb->ki_pos + iter->count - pg_pos; if (PageReadahead(page)) { if (iocb->ki_flags & IOCB_NOIO) { - for (j = i; j < pvec->nr; j++) - put_page(pvec->pages[j]); - pvec->nr = i; + put_page(page); + pvec->nr--; err = -EAGAIN; - break; + goto err; } page_cache_async_readahead(mapping, ra, filp, page, pg_index, last_index - pg_index); @@ -2378,26 +2424,23 @@ got_pages: if (!PageUptodate(page)) { if ((iocb->ki_flags & IOCB_NOWAIT) || - ((iocb->ki_flags & IOCB_WAITQ) && i)) { - for (j = i; j < pvec->nr; j++) - put_page(pvec->pages[j]); - pvec->nr = i; + ((iocb->ki_flags & IOCB_WAITQ) && pvec->nr > 1)) { + put_page(page); + pvec->nr--; err = -EAGAIN; - break; + goto err; } page = filemap_update_page(iocb, filp, iter, page, pg_pos, pg_count); if (IS_ERR_OR_NULL(page)) { - for (j = i + 1; j < pvec->nr; j++) - put_page(pvec->pages[j]); - pvec->nr = i; + pvec->nr--; err = PTR_ERR_OR_ZERO(page); - break; } } } +err: if (likely(pvec->nr)) return 0; if (err) @@ -2442,6 +2485,7 @@ ssize_t generic_file_buffered_read(struc return 0; iov_iter_truncate(iter, inode->i_sb->s_maxbytes); + pagevec_init(&pvec); do { cond_resched(); @@ -2469,13 +2513,8 @@ ssize_t generic_file_buffered_read(struc isize = i_size_read(inode); if (unlikely(iocb->ki_pos >= isize)) goto put_pages; - end_offset = min_t(loff_t, isize, iocb->ki_pos + iter->count); - while ((iocb->ki_pos >> PAGE_SHIFT) + pvec.nr > - (end_offset + PAGE_SIZE - 1) >> PAGE_SHIFT) - put_page(pvec.pages[--pvec.nr]); - /* * Once we start copying data, we don't want to be touching any * cachelines that might be contended: @@ -2489,24 +2528,32 @@ ssize_t generic_file_buffered_read(struc if (iocb->ki_pos >> PAGE_SHIFT != ra->prev_pos >> PAGE_SHIFT) mark_page_accessed(pvec.pages[0]); - for (i = 1; i < pagevec_count(&pvec); i++) - mark_page_accessed(pvec.pages[i]); for (i = 0; i < pagevec_count(&pvec); i++) { - unsigned int offset = iocb->ki_pos & ~PAGE_MASK; - unsigned int bytes = min_t(loff_t, end_offset - iocb->ki_pos, - PAGE_SIZE - offset); - unsigned int copied; + struct page *page = pvec.pages[i]; + size_t page_size = thp_size(page); + size_t offset = iocb->ki_pos & (page_size - 1); + size_t bytes = min_t(loff_t, end_offset - iocb->ki_pos, + page_size - offset); + size_t copied; + if (end_offset < page_offset(page)) + break; + if (i > 0) + mark_page_accessed(page); /* * If users can be writing to this page using arbitrary * virtual addresses, take care about potential aliasing * before reading the page on the kernel side. */ - if (writably_mapped) - flush_dcache_page(pvec.pages[i]); + if (writably_mapped) { + int j; + + for (j = 0; j < thp_nr_pages(page); j++) + flush_dcache_page(page + j); + } - copied = copy_page_to_iter(pvec.pages[i], offset, bytes, iter); + copied = copy_page_to_iter(page, offset, bytes, iter); written += copied; iocb->ki_pos += copied; @@ -2520,6 +2567,7 @@ ssize_t generic_file_buffered_read(struc put_pages: for (i = 0; i < pagevec_count(&pvec); i++) put_page(pvec.pages[i]); + pagevec_reinit(&pvec); } while (iov_iter_count(iter) && iocb->ki_pos < isize && !error); file_accessed(filp); _
