On Tue, Nov 03, 2020 at 08:57:36AM +0100, Christoph Hellwig wrote:
> On Mon, Nov 02, 2020 at 06:43:09PM +0000, Matthew Wilcox (Oracle) wrote:
> > Avoid a goto, and by the time we get to calling filemap_update_page(),
> > we definitely have at least one page.
>
> I find the error handling flow hard to follow and the existing but
> heavily touched naming of the nr_got variable and the find_pages label
> not helpful. I'd do the following on top of this patch:
I've removed nr_got entirely in my current tree ...
diff --git a/mm/filemap.c b/mm/filemap.c
index 8264bcdb99f4..ea0cd0df638b 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2166,21 +2166,17 @@ static void shrink_readahead_size_eio(struct file_ra_state *ra)
ra->ra_pages /= 4;
}
-static unsigned mapping_get_read_thps(struct address_space *mapping,
- pgoff_t index, unsigned int nr_pages, struct page **pages)
+static void mapping_get_read_thps(struct address_space *mapping,
+ pgoff_t index, pgoff_t max, struct pagevec *pvec)
{
XA_STATE(xas, &mapping->i_pages, index);
struct page *head;
- unsigned int ret = 0;
-
- if (unlikely(!nr_pages))
- return 0;
rcu_read_lock();
for (head = xas_load(&xas); head; head = xas_next(&xas)) {
if (xas_retry(&xas, head))
continue;
- if (xa_is_value(head))
+ if (xas.xa_index > max || xa_is_value(head))
break;
if (!page_cache_get_speculative(head))
goto retry;
@@ -2189,8 +2185,7 @@ static unsigned mapping_get_read_thps(struct address_space *mapping,
if (unlikely(head != xas_reload(&xas)))
goto put_page;
- pages[ret++] = head;
- if (ret == nr_pages)
+ if (!pagevec_add(pvec, head))
break;
if (!PageUptodate(head))
break;
@@ -2205,7 +2200,6 @@ static unsigned mapping_get_read_thps(struct address_space *mapping,
xas_reset(&xas);
}
rcu_read_unlock();
- return ret;
}
static int filemap_read_page(struct file *file, struct address_space *mapping,
@@ -2343,52 +2337,53 @@ static int filemap_readahead(struct kiocb *iocb, struct file *file,
}
static int filemap_get_pages(struct kiocb *iocb, struct iov_iter *iter,
- struct page **pages, unsigned int nr)
+ struct pagevec *pvec)
{
struct file *filp = iocb->ki_filp;
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;
+ pgoff_t maxindex = DIV_ROUND_UP(iocb->ki_pos + iter->count, PAGE_SIZE);
struct page *page;
- int nr_got, err = 0;
+ int err = 0;
- nr = min_t(unsigned long, last_index - index, nr);
find_page:
if (fatal_signal_pending(current))
return -EINTR;
- nr_got = mapping_get_read_thps(mapping, index, nr, pages);
- if (!nr_got) {
+ pagevec_init(pvec);
+ mapping_get_read_thps(mapping, index, maxindex, pvec);
+ if (!pagevec_count(pvec)) {
if (iocb->ki_flags & IOCB_NOIO)
return -EAGAIN;
page_cache_sync_readahead(mapping, ra, filp, index,
- last_index - index);
- nr_got = mapping_get_read_thps(mapping, index, nr, pages);
+ maxindex - index);
+ mapping_get_read_thps(mapping, index, maxindex, pvec);
}
- if (!nr_got) {
+ if (!pagevec_count(pvec)) {
if (iocb->ki_flags & (IOCB_NOWAIT | IOCB_WAITQ))
return -EAGAIN;
- pages[0] = filemap_create_page(filp, mapping,
+ page = filemap_create_page(filp, mapping,
iocb->ki_pos >> PAGE_SHIFT);
- if (!pages[0])
+ if (!page)
goto find_page;
- if (IS_ERR(pages[0]))
- return PTR_ERR(pages[0]);
- return 1;
+ if (IS_ERR(page))
+ return PTR_ERR(page);
+ pagevec_add(pvec, page);
+ return 0;
}
- page = pages[nr_got - 1];
+ page = pvec->pages[pagevec_count(pvec) - 1];
if (PageReadahead(page))
- err = filemap_readahead(iocb, filp, mapping, page, last_index);
+ err = filemap_readahead(iocb, filp, mapping, page, maxindex);
if (!err && !PageUptodate(page))
err = filemap_update_page(iocb, mapping, iter, page,
- nr_got == 1);
+ pagevec_count(pvec) == 1);
if (err)
- nr_got--;
- if (likely(nr_got))
- return nr_got;
+ pvec->nr--;
+ if (likely(pagevec_count(pvec)))
+ return 0;
if (err < 0)
return err;
err = 0;
@@ -2418,11 +2413,8 @@ ssize_t filemap_read(struct kiocb *iocb, struct iov_iter *iter,
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,
- ((iocb->ki_pos + iter->count + PAGE_SIZE - 1) >> PAGE_SHIFT) -
- (iocb->ki_pos >> PAGE_SHIFT));
- int i, pg_nr, error = 0;
+ struct pagevec pvec;
+ int i, error = 0;
bool writably_mapped;
loff_t isize, end_offset;
@@ -2430,14 +2422,6 @@ ssize_t filemap_read(struct kiocb *iocb, struct iov_iter *iter,
return 0;
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();
@@ -2449,12 +2433,9 @@ ssize_t filemap_read(struct kiocb *iocb, struct iov_iter *iter,
if ((iocb->ki_flags & IOCB_WAITQ) && already_read)
iocb->ki_flags |= IOCB_NOWAIT;
- i = 0;
- pg_nr = filemap_get_pages(iocb, iter, pages, nr_pages);
- if (pg_nr < 0) {
- error = pg_nr;
+ error = filemap_get_pages(iocb, iter, &pvec);
+ if (error < 0)
break;
- }
/*
* i_size must be checked after we know the pages are Uptodate.
@@ -2467,13 +2448,8 @@ ssize_t filemap_read(struct kiocb *iocb, struct iov_iter *iter,
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) + pg_nr >
- (end_offset + PAGE_SIZE - 1) >> PAGE_SHIFT)
- put_page(pages[--pg_nr]);
-
/*
* Once we start copying data, we don't want to be touching any
* cachelines that might be contended:
@@ -2486,18 +2462,20 @@ ssize_t filemap_read(struct kiocb *iocb, struct iov_iter *iter,
*/
if (iocb->ki_pos >> PAGE_SHIFT !=
ra->prev_pos >> PAGE_SHIFT)
- mark_page_accessed(pages[0]);
- for (i = 1; i < pg_nr; i++)
- mark_page_accessed(pages[i]);
+ mark_page_accessed(pvec.pages[0]);
- for (i = 0; i < pg_nr; i++) {
- struct page *page = pages[i];
+ for (i = 0; i < pagevec_count(&pvec); i++) {
+ 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
@@ -2522,15 +2500,11 @@ ssize_t filemap_read(struct kiocb *iocb, struct iov_iter *iter,
}
}
put_pages:
- for (i = 0; i < pg_nr; i++)
- put_page(pages[i]);
+ pagevec_release(&pvec);
} while (iov_iter_count(iter) && iocb->ki_pos < isize && !error);
file_accessed(filp);
- if (pages != pages_onstack)
- kfree(pages);
-
return already_read ? already_read : error;
}
EXPORT_SYMBOL_GPL(filemap_read);
I like a lot of the restructuring you did there. I'll incorporate it.
