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new helper: iov_iter_get_pages()
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iov_iter_get_pages(iter, pages, maxsize, &start) grabs references pinning
the pages of up to maxsize of (contiguous) data from iter.  Returns the
amount of memory grabbed or -error.  In case of success, the requested
area begins at offset start in pages[0] and runs through pages[1], etc.
Less than requested amount might be returned - either because the contiguous
area in the beginning of iterator is smaller than requested, or because
the kernel failed to pin that many pages.

direct-io.c switched to using iov_iter_get_pages()

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
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Al Viro committed May 6, 2014
1 parent 3320c60 commit 7b2c99d
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Showing 3 changed files with 67 additions and 73 deletions.
111 changes: 38 additions & 73 deletions fs/direct-io.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -77,7 +77,6 @@ struct dio_submit {
unsigned blocks_available; /* At block_in_file. changes */
int reap_counter; /* rate limit reaping */
sector_t final_block_in_request;/* doesn't change */
unsigned first_block_in_page; /* doesn't change, Used only once */
int boundary; /* prev block is at a boundary */
get_block_t *get_block; /* block mapping function */
dio_submit_t *submit_io; /* IO submition function */
Expand All @@ -98,19 +97,14 @@ struct dio_submit {
sector_t cur_page_block; /* Where it starts */
loff_t cur_page_fs_offset; /* Offset in file */

/*
* Page fetching state. These variables belong to dio_refill_pages().
*/
int curr_page; /* changes */
int total_pages; /* doesn't change */
unsigned long curr_user_address;/* changes */

struct iov_iter *iter;
/*
* Page queue. These variables belong to dio_refill_pages() and
* dio_get_page().
*/
unsigned head; /* next page to process */
unsigned tail; /* last valid page + 1 */
size_t from, to;
};

/* dio_state communicated between submission path and end_io */
Expand Down Expand Up @@ -163,15 +157,10 @@ static inline unsigned dio_pages_present(struct dio_submit *sdio)
*/
static inline int dio_refill_pages(struct dio *dio, struct dio_submit *sdio)
{
int ret;
int nr_pages;
ssize_t ret;

nr_pages = min(sdio->total_pages - sdio->curr_page, DIO_PAGES);
ret = get_user_pages_fast(
sdio->curr_user_address, /* Where from? */
nr_pages, /* How many pages? */
dio->rw == READ, /* Write to memory? */
&dio->pages[0]); /* Put results here */
ret = iov_iter_get_pages(sdio->iter, dio->pages, DIO_PAGES * PAGE_SIZE,
&sdio->from);

if (ret < 0 && sdio->blocks_available && (dio->rw & WRITE)) {
struct page *page = ZERO_PAGE(0);
Expand All @@ -186,18 +175,19 @@ static inline int dio_refill_pages(struct dio *dio, struct dio_submit *sdio)
dio->pages[0] = page;
sdio->head = 0;
sdio->tail = 1;
ret = 0;
goto out;
sdio->from = 0;
sdio->to = PAGE_SIZE;
return 0;
}

if (ret >= 0) {
sdio->curr_user_address += ret * PAGE_SIZE;
sdio->curr_page += ret;
iov_iter_advance(sdio->iter, ret);
ret += sdio->from;
sdio->head = 0;
sdio->tail = ret;
ret = 0;
sdio->tail = (ret + PAGE_SIZE - 1) / PAGE_SIZE;
sdio->to = ((ret - 1) & (PAGE_SIZE - 1)) + 1;
return 0;
}
out:
return ret;
}

Expand All @@ -208,8 +198,9 @@ static inline int dio_refill_pages(struct dio *dio, struct dio_submit *sdio)
* L1 cache.
*/
static inline struct page *dio_get_page(struct dio *dio,
struct dio_submit *sdio)
struct dio_submit *sdio, size_t *from, size_t *to)
{
int n;
if (dio_pages_present(sdio) == 0) {
int ret;

Expand All @@ -218,7 +209,10 @@ static inline struct page *dio_get_page(struct dio *dio,
return ERR_PTR(ret);
BUG_ON(dio_pages_present(sdio) == 0);
}
return dio->pages[sdio->head++];
n = sdio->head++;
*from = n ? 0 : sdio->from;
*to = (n == sdio->tail - 1) ? sdio->to : PAGE_SIZE;
return dio->pages[n];
}

/**
Expand Down Expand Up @@ -422,8 +416,8 @@ static inline void dio_bio_submit(struct dio *dio, struct dio_submit *sdio)
*/
static inline void dio_cleanup(struct dio *dio, struct dio_submit *sdio)
{
while (dio_pages_present(sdio))
page_cache_release(dio_get_page(dio, sdio));
while (sdio->head < sdio->tail)
page_cache_release(dio->pages[sdio->head++]);
}

/*
Expand Down Expand Up @@ -912,23 +906,18 @@ static int do_direct_IO(struct dio *dio, struct dio_submit *sdio,
struct buffer_head *map_bh)
{
const unsigned blkbits = sdio->blkbits;
const unsigned blocks_per_page = PAGE_SIZE >> blkbits;
struct page *page;
unsigned block_in_page;
int ret = 0;

/* The I/O can start at any block offset within the first page */
block_in_page = sdio->first_block_in_page;

while (sdio->block_in_file < sdio->final_block_in_request) {
page = dio_get_page(dio, sdio);
struct page *page;
size_t from, to;
page = dio_get_page(dio, sdio, &from, &to);
if (IS_ERR(page)) {
ret = PTR_ERR(page);
goto out;
}

while (block_in_page < blocks_per_page) {
unsigned offset_in_page = block_in_page << blkbits;
while (from < to) {
unsigned this_chunk_bytes; /* # of bytes mapped */
unsigned this_chunk_blocks; /* # of blocks */
unsigned u;
Expand Down Expand Up @@ -999,10 +988,9 @@ static int do_direct_IO(struct dio *dio, struct dio_submit *sdio,
page_cache_release(page);
goto out;
}
zero_user(page, block_in_page << blkbits,
1 << blkbits);
zero_user(page, from, 1 << blkbits);
sdio->block_in_file++;
block_in_page++;
from += 1 << blkbits;
dio->result += 1 << blkbits;
goto next_block;
}
Expand All @@ -1020,7 +1008,7 @@ static int do_direct_IO(struct dio *dio, struct dio_submit *sdio,
* can add to this page
*/
this_chunk_blocks = sdio->blocks_available;
u = (PAGE_SIZE - offset_in_page) >> blkbits;
u = (to - from) >> blkbits;
if (this_chunk_blocks > u)
this_chunk_blocks = u;
u = sdio->final_block_in_request - sdio->block_in_file;
Expand All @@ -1032,7 +1020,7 @@ static int do_direct_IO(struct dio *dio, struct dio_submit *sdio,
if (this_chunk_blocks == sdio->blocks_available)
sdio->boundary = buffer_boundary(map_bh);
ret = submit_page_section(dio, sdio, page,
offset_in_page,
from,
this_chunk_bytes,
sdio->next_block_for_io,
map_bh);
Expand All @@ -1043,9 +1031,9 @@ static int do_direct_IO(struct dio *dio, struct dio_submit *sdio,
sdio->next_block_for_io += this_chunk_blocks;

sdio->block_in_file += this_chunk_blocks;
block_in_page += this_chunk_blocks;
from += this_chunk_bytes;
dio->result += this_chunk_bytes;
sdio->blocks_available -= this_chunk_blocks;
dio->result += this_chunk_blocks << blkbits;
next_block:
BUG_ON(sdio->block_in_file > sdio->final_block_in_request);
if (sdio->block_in_file == sdio->final_block_in_request)
Expand All @@ -1054,7 +1042,6 @@ static int do_direct_IO(struct dio *dio, struct dio_submit *sdio,

/* Drop the ref which was taken in get_user_pages() */
page_cache_release(page);
block_in_page = 0;
}
out:
return ret;
Expand Down Expand Up @@ -1122,7 +1109,6 @@ do_blockdev_direct_IO(int rw, struct kiocb *iocb, struct inode *inode,
struct dio *dio;
struct dio_submit sdio = { 0, };
unsigned long user_addr;
size_t bytes;
struct buffer_head map_bh = { 0, };
struct blk_plug plug;
unsigned long align = offset | iov_iter_alignment(iter);
Expand Down Expand Up @@ -1234,6 +1220,10 @@ do_blockdev_direct_IO(int rw, struct kiocb *iocb, struct inode *inode,
spin_lock_init(&dio->bio_lock);
dio->refcount = 1;

sdio.iter = iter;
sdio.final_block_in_request =
(offset + iov_iter_count(iter)) >> blkbits;

/*
* In case of non-aligned buffers, we may need 2 more
* pages since we need to zero out first and last block.
Expand All @@ -1250,34 +1240,9 @@ do_blockdev_direct_IO(int rw, struct kiocb *iocb, struct inode *inode,

blk_start_plug(&plug);

for (seg = 0; seg < iter->nr_segs; seg++) {
user_addr = (unsigned long)iter->iov[seg].iov_base;
sdio.size += bytes = iter->iov[seg].iov_len;

/* Index into the first page of the first block */
sdio.first_block_in_page = (user_addr & ~PAGE_MASK) >> blkbits;
sdio.final_block_in_request = sdio.block_in_file +
(bytes >> blkbits);
/* Page fetching state */
sdio.head = 0;
sdio.tail = 0;
sdio.curr_page = 0;

sdio.total_pages = 0;
if (user_addr & (PAGE_SIZE-1)) {
sdio.total_pages++;
bytes -= PAGE_SIZE - (user_addr & (PAGE_SIZE - 1));
}
sdio.total_pages += (bytes + PAGE_SIZE - 1) / PAGE_SIZE;
sdio.curr_user_address = user_addr;

retval = do_direct_IO(dio, &sdio, &map_bh);

if (retval) {
dio_cleanup(dio, &sdio);
break;
}
} /* end iovec loop */
retval = do_direct_IO(dio, &sdio, &map_bh);
if (retval)
dio_cleanup(dio, &sdio);

if (retval == -ENOTBLK) {
/*
Expand Down
2 changes: 2 additions & 0 deletions include/linux/uio.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -71,6 +71,8 @@ size_t copy_page_to_iter(struct page *page, size_t offset, size_t bytes,
unsigned long iov_iter_alignment(const struct iov_iter *i);
void iov_iter_init(struct iov_iter *i, int direction, const struct iovec *iov,
unsigned long nr_segs, size_t count);
ssize_t iov_iter_get_pages(struct iov_iter *i, struct page **pages,
size_t maxsize, size_t *start);

static inline size_t iov_iter_count(struct iov_iter *i)
{
Expand Down
27 changes: 27 additions & 0 deletions mm/iov_iter.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -235,3 +235,30 @@ void iov_iter_init(struct iov_iter *i, int direction,
i->count = count;
}
EXPORT_SYMBOL(iov_iter_init);

ssize_t iov_iter_get_pages(struct iov_iter *i,
struct page **pages, size_t maxsize,
size_t *start)
{
size_t offset = i->iov_offset;
const struct iovec *iov = i->iov;
size_t len;
unsigned long addr;
int n;
int res;

len = iov->iov_len - offset;
if (len > i->count)
len = i->count;
if (len > maxsize)
len = maxsize;
addr = (unsigned long)iov->iov_base + offset;
len += *start = addr & (PAGE_SIZE - 1);
addr &= ~(PAGE_SIZE - 1);
n = (len + PAGE_SIZE - 1) / PAGE_SIZE;
res = get_user_pages_fast(addr, n, (i->type & WRITE) != WRITE, pages);
if (unlikely(res < 0))
return res;
return (res == n ? len : res * PAGE_SIZE) - *start;
}
EXPORT_SYMBOL(iov_iter_get_pages);

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