[PATCH v3 09/59] afs: Don't use folio->private to record partial modification

David Howells
2023-12-07T21:22:51Z

AFS currently uses folio->private to store the range of bytes within a
folio that have been modified - the idea being that if we have, say, a 2MiB
folio and someone writes a single byte, we only have to write back that
single page and not the whole 2MiB folio - thereby saving on network
bandwidth.

Remove this, at least for now, and accept the extra network load (which
doesn't matter in the common case of writing a whole file at a time from
beginning to end).

This makes folio->private available for netfslib to use.

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Marc Dionne <marc.dionne@auristor.com>
cc: Jeff Layton <jlayton@kernel.org>
cc: linux-afs@lists.infradead.org
cc: linux-cachefs@redhat.com
cc: linux-fsdevel@vger.kernel.org
cc: linux-mm@kvack.org
---
fs/afs/file.c | 67 -------------
fs/afs/internal.h | 56 -----------
fs/afs/write.c | 188 ++++++++-----------------------------
include/trace/events/afs.h | 16 +---
4 files changed, 42 insertions(+), 285 deletions(-)

diff --git a/fs/afs/file.c b/fs/afs/file.c
index 9142fda7dbd6..0d783e5b2147 100644
--- a/fs/afs/file.c
+++ b/fs/afs/file.c
@@ -386,63 +386,6 @@ const struct netfs_request_ops afs_req_ops = {
.issue_read = afs_issue_read,
};

-/*
- * Adjust the dirty region of the page on truncation or full invalidation,
- * getting rid of the markers altogether if the region is entirely invalidated.
- */
-static void afs_invalidate_dirty(struct folio *folio, size_t offset,
- size_t length)
-{
- struct afs_vnode *vnode = AFS_FS_I(folio_inode(folio));
- unsigned long priv;
- unsigned int f, t, end = offset + length;
-
- priv = (unsigned long)folio_get_private(folio);
-
- /* we clean up only if the entire page is being invalidated */
- if (offset == 0 && length == folio_size(folio))
- goto full_invalidate;
-
- /* If the page was dirtied by page_mkwrite(), the PTE stays writable
- * and we don't get another notification to tell us to expand it
- * again.
- */
- if (afs_is_folio_dirty_mmapped(priv))
- return;
-
- /* We may need to shorten the dirty region */
- f = afs_folio_dirty_from(folio, priv);
- t = afs_folio_dirty_to(folio, priv);
-
- if (t <= offset || f >= end)
- return; /* Doesn't overlap */
-
- if (f < offset && t > end)
- return; /* Splits the dirty region - just absorb it */
-
- if (f >= offset && t <= end)
- goto undirty;
-
- if (f < offset)
- t = offset;
- else
- f = end;
- if (f == t)
- goto undirty;
-
- priv = afs_folio_dirty(folio, f, t);
- folio_change_private(folio, (void *)priv);
- trace_afs_folio_dirty(vnode, tracepoint_string("trunc"), folio);
- return;
-
-undirty:
- trace_afs_folio_dirty(vnode, tracepoint_string("undirty"), folio);
- folio_clear_dirty_for_io(folio);
-full_invalidate:
- trace_afs_folio_dirty(vnode, tracepoint_string("inval"), folio);
- folio_detach_private(folio);
-}
-
/*
* invalidate part or all of a page
* - release a page and clean up its private data if offset is 0 (indicating
@@ -453,11 +396,6 @@ static void afs_invalidate_folio(struct folio *folio, size_t offset,
{
_enter("{%lu},%zu,%zu", folio->index, offset, length);

- BUG_ON(!folio_test_locked(folio));
-
- if (folio_get_private(folio))
- afs_invalidate_dirty(folio, offset, length);
-
folio_wait_fscache(folio);
_leave("");
}
@@ -485,11 +423,6 @@ static bool afs_release_folio(struct folio *folio, gfp_t gfp)
fscache_note_page_release(afs_vnode_cache(vnode));
#endif

- if (folio_test_private(folio)) {
- trace_afs_folio_dirty(vnode, tracepoint_string("rel"), folio);
- folio_detach_private(folio);
- }
-
/* Indicate that the folio can be released */
_leave(" = T");
return true;
diff --git a/fs/afs/internal.h b/fs/afs/internal.h
index ba25a75609a2..ec173e58ddfe 100644
--- a/fs/afs/internal.h
+++ b/fs/afs/internal.h
@@ -893,62 +893,6 @@ static inline void afs_invalidate_cache(struct afs_vnode *vnode, unsigned int fl
i_size_read(&vnode->netfs.inode), flags);
}

-/*
- * We use folio->private to hold the amount of the folio that we've written to,
- * splitting the field into two parts. However, we need to represent a range
- * 0...FOLIO_SIZE, so we reduce the resolution if the size of the folio
- * exceeds what we can encode.
- */
-#ifdef CONFIG_64BIT
-#define __AFS_FOLIO_PRIV_MASK 0x7fffffffUL
-#define __AFS_FOLIO_PRIV_SHIFT 32
-#define __AFS_FOLIO_PRIV_MMAPPED 0x80000000UL
-#else
-#define __AFS_FOLIO_PRIV_MASK 0x7fffUL
-#define __AFS_FOLIO_PRIV_SHIFT 16
-#define __AFS_FOLIO_PRIV_MMAPPED 0x8000UL
-#endif
-
-static inline unsigned int afs_folio_dirty_resolution(struct folio *folio)
-{
- int shift = folio_shift(folio) - (__AFS_FOLIO_PRIV_SHIFT - 1);
- return (shift > 0) ? shift : 0;
-}
-
-static inline size_t afs_folio_dirty_from(struct folio *folio, unsigned long priv)
-{
- unsigned long x = priv & __AFS_FOLIO_PRIV_MASK;
-
- /* The lower bound is inclusive */
- return x << afs_folio_dirty_resolution(folio);
-}
-
-static inline size_t afs_folio_dirty_to(struct folio *folio, unsigned long priv)
-{
- unsigned long x = (priv >> __AFS_FOLIO_PRIV_SHIFT) & __AFS_FOLIO_PRIV_MASK;
-
- /* The upper bound is immediately beyond the region */
- return (x + 1) << afs_folio_dirty_resolution(folio);
-}
-
-static inline unsigned long afs_folio_dirty(struct folio *folio, size_t from, size_t to)
-{
- unsigned int res = afs_folio_dirty_resolution(folio);
- from >>= res;
- to = (to - 1) >> res;
- return (to << __AFS_FOLIO_PRIV_SHIFT) | from;
-}
-
-static inline unsigned long afs_folio_dirty_mmapped(unsigned long priv)
-{
- return priv | __AFS_FOLIO_PRIV_MMAPPED;
-}
-
-static inline bool afs_is_folio_dirty_mmapped(unsigned long priv)
-{
- return priv & __AFS_FOLIO_PRIV_MMAPPED;
-}
-
#include <trace/events/afs.h>

/*****************************************************************************/
diff --git a/fs/afs/write.c b/fs/afs/write.c
index 7354aa5775fc..6aa272acb95c 100644
--- a/fs/afs/write.c
+++ b/fs/afs/write.c
@@ -16,7 +16,8 @@

static int afs_writepages_region(struct address_space *mapping,
struct writeback_control *wbc,
- loff_t start, loff_t end, loff_t *_next,
+ unsigned long long start,
+ unsigned long long end, loff_t *_next,
bool max_one_loop);

static void afs_write_to_cache(struct afs_vnode *vnode, loff_t start, size_t len,
@@ -34,25 +35,6 @@ static void afs_folio_start_fscache(bool caching, struct folio *folio)
}
#endif

-/*
- * Flush out a conflicting write. This may extend the write to the surrounding
- * pages if also dirty and contiguous to the conflicting region..
- */
-static int afs_flush_conflicting_write(struct address_space *mapping,
- struct folio *folio)
-{
- struct writeback_control wbc = {
- .sync_mode = WB_SYNC_ALL,
- .nr_to_write = LONG_MAX,
- .range_start = folio_pos(folio),
- .range_end = LLONG_MAX,
- };
- loff_t next;
-
- return afs_writepages_region(mapping, &wbc, folio_pos(folio), LLONG_MAX,
- &next, true);
-}
-
/*
* prepare to perform part of a write to a page
*/
@@ -62,10 +44,6 @@ int afs_write_begin(struct file *file, struct address_space *mapping,
{
struct afs_vnode *vnode = AFS_FS_I(file_inode(file));
struct folio *folio;
- unsigned long priv;
- unsigned f, from;
- unsigned t, to;
- pgoff_t index;
int ret;

_enter("{%llx:%llu},%llx,%x",
@@ -79,49 +57,20 @@ int afs_write_begin(struct file *file, struct address_space *mapping,
if (ret < 0)
return ret;

- index = folio_index(folio);
- from = pos - index * PAGE_SIZE;
- to = from + len;
-
try_again:
/* See if this page is already partially written in a way that we can
* merge the new write with.
*/
- if (folio_test_private(folio)) {
- priv = (unsigned long)folio_get_private(folio);
- f = afs_folio_dirty_from(folio, priv);
- t = afs_folio_dirty_to(folio, priv);
- ASSERTCMP(f, <=, t);
-
- if (folio_test_writeback(folio)) {
- trace_afs_folio_dirty(vnode, tracepoint_string("alrdy"), folio);
- folio_unlock(folio);
- goto wait_for_writeback;
- }
- /* If the file is being filled locally, allow inter-write
- * spaces to be merged into writes. If it's not, only write
- * back what the user gives us.
- */
- if (!test_bit(AFS_VNODE_NEW_CONTENT, &vnode->flags) &&
- (to < f || from > t))
- goto flush_conflicting_write;
+ if (folio_test_writeback(folio)) {
+ trace_afs_folio_dirty(vnode, tracepoint_string("alrdy"), folio);
+ folio_unlock(folio);
+ goto wait_for_writeback;
}

*_page = folio_file_page(folio, pos / PAGE_SIZE);
_leave(" = 0");
return 0;

- /* The previous write and this write aren't adjacent or overlapping, so
- * flush the page out.
- */
-flush_conflicting_write:
- trace_afs_folio_dirty(vnode, tracepoint_string("confl"), folio);
- folio_unlock(folio);
-
- ret = afs_flush_conflicting_write(mapping, folio);
- if (ret < 0)
- goto error;
-
wait_for_writeback:
ret = folio_wait_writeback_killable(folio);
if (ret < 0)
@@ -147,9 +96,6 @@ int afs_write_end(struct file *file, struct address_space *mapping,
{
struct folio *folio = page_folio(subpage);
struct afs_vnode *vnode = AFS_FS_I(file_inode(file));
- unsigned long priv;
- unsigned int f, from = offset_in_folio(folio, pos);
- unsigned int t, to = from + copied;
loff_t i_size, write_end_pos;

_enter("{%llx:%llu},{%lx}",
@@ -179,23 +125,6 @@ int afs_write_end(struct file *file, struct address_space *mapping,
fscache_update_cookie(afs_vnode_cache(vnode), NULL, &write_end_pos);
}

- if (folio_test_private(folio)) {
- priv = (unsigned long)folio_get_private(folio);
- f = afs_folio_dirty_from(folio, priv);
- t = afs_folio_dirty_to(folio, priv);
- if (from < f)
- f = from;
- if (to > t)
- t = to;
- priv = afs_folio_dirty(folio, f, t);
- folio_change_private(folio, (void *)priv);
- trace_afs_folio_dirty(vnode, tracepoint_string("dirty+"), folio);
- } else {
- priv = afs_folio_dirty(folio, from, to);
- folio_attach_private(folio, (void *)priv);
- trace_afs_folio_dirty(vnode, tracepoint_string("dirty"), folio);
- }
-
if (folio_mark_dirty(folio))
_debug("dirtied %lx", folio_index(folio));

@@ -300,7 +229,6 @@ static void afs_pages_written_back(struct afs_vnode *vnode, loff_t start, unsign
}

trace_afs_folio_dirty(vnode, tracepoint_string("clear"), folio);
- folio_detach_private(folio);
folio_end_writeback(folio);
}

@@ -454,17 +382,12 @@ static void afs_extend_writeback(struct address_space *mapping,
long *_count,
loff_t start,
loff_t max_len,
- bool new_content,
bool caching,
- unsigned int *_len)
+ size_t *_len)
{
struct folio_batch fbatch;
struct folio *folio;
- unsigned long priv;
- unsigned int psize, filler = 0;
- unsigned int f, t;
- loff_t len = *_len;
- pgoff_t index = (start + len) / PAGE_SIZE;
+ pgoff_t index = (start + *_len) / PAGE_SIZE;
bool stop = true;
unsigned int i;

@@ -492,7 +415,7 @@ static void afs_extend_writeback(struct address_space *mapping,
continue;
}

- /* Has the page moved or been split? */
+ /* Has the folio moved or been split? */
if (unlikely(folio != xas_reload(&xas))) {
folio_put(folio);
break;
@@ -510,24 +433,13 @@ static void afs_extend_writeback(struct address_space *mapping,
break;
}

- psize = folio_size(folio);
- priv = (unsigned long)folio_get_private(folio);
- f = afs_folio_dirty_from(folio, priv);
- t = afs_folio_dirty_to(folio, priv);
- if (f != 0 && !new_content) {
- folio_unlock(folio);
- folio_put(folio);
- break;
- }
-
- len += filler + t;
- filler = psize - t;
- if (len >= max_len || *_count <= 0)
+ index += folio_nr_pages(folio);
+ *_count -= folio_nr_pages(folio);
+ *_len += folio_size(folio);
+ stop = false;
+ if (*_len >= max_len || *_count <= 0)
stop = true;
- else if (t == psize || new_content)
- stop = false;

- index += folio_nr_pages(folio);
if (!folio_batch_add(&fbatch, folio))
break;
if (stop)
@@ -552,16 +464,12 @@ static void afs_extend_writeback(struct address_space *mapping,
BUG();
folio_start_writeback(folio);
afs_folio_start_fscache(caching, folio);
-
- *_count -= folio_nr_pages(folio);
folio_unlock(folio);
}

folio_batch_release(&fbatch);
cond_resched();
} while (!stop);
-
- *_len = len;
}

/*
@@ -571,14 +479,13 @@ static void afs_extend_writeback(struct address_space *mapping,
static ssize_t afs_write_back_from_locked_folio(struct address_space *mapping,
struct writeback_control *wbc,
struct folio *folio,
- loff_t start, loff_t end)
+ unsigned long long start,
+ unsigned long long end)
{
struct afs_vnode *vnode = AFS_FS_I(mapping->host);
struct iov_iter iter;
- unsigned long priv;
- unsigned int offset, to, len, max_len;
- loff_t i_size = i_size_read(&vnode->netfs.inode);
- bool new_content = test_bit(AFS_VNODE_NEW_CONTENT, &vnode->flags);
+ unsigned long long i_size = i_size_read(&vnode->netfs.inode);
+ size_t len, max_len;
bool caching = fscache_cookie_enabled(afs_vnode_cache(vnode));
long count = wbc->nr_to_write;
int ret;
@@ -595,13 +502,9 @@ static ssize_t afs_write_back_from_locked_folio(struct address_space *mapping,
* immediately lockable, is not dirty or is missing, or we reach the
* end of the range.
*/
- priv = (unsigned long)folio_get_private(folio);
- offset = afs_folio_dirty_from(folio, priv);
- to = afs_folio_dirty_to(folio, priv);
trace_afs_folio_dirty(vnode, tracepoint_string("store"), folio);

- len = to - offset;
- start += offset;
+ len = folio_size(folio);
if (start < i_size) {
/* Trim the write to the EOF; the extra data is ignored. Also
* put an upper limit on the size of a single storedata op.
@@ -610,12 +513,10 @@ static ssize_t afs_write_back_from_locked_folio(struct address_space *mapping,
max_len = min_t(unsigned long long, max_len, end - start + 1);
max_len = min_t(unsigned long long, max_len, i_size - start);

- if (len < max_len &&
- (to == folio_size(folio) || new_content))
+ if (len < max_len)
afs_extend_writeback(mapping, vnode, &count,
- start, max_len, new_content,
- caching, &len);
- len = min_t(loff_t, len, max_len);
+ start, max_len, caching, &len);
+ len = min_t(unsigned long long, len, i_size - start);
}

/* We now have a contiguous set of dirty pages, each with writeback
@@ -625,7 +526,7 @@ static ssize_t afs_write_back_from_locked_folio(struct address_space *mapping,
folio_unlock(folio);

if (start < i_size) {
- _debug("write back %x @%llx [%llx]", len, start, i_size);
+ _debug("write back %zx @%llx [%llx]", len, start, i_size);

/* Speculatively write to the cache. We have to fix this up
* later if the store fails.
@@ -635,7 +536,7 @@ static ssize_t afs_write_back_from_locked_folio(struct address_space *mapping,
iov_iter_xarray(&iter, ITER_SOURCE, &mapping->i_pages, start, len);
ret = afs_store_data(vnode, &iter, start, false);
} else {
- _debug("write discard %x @%llx [%llx]", len, start, i_size);
+ _debug("write discard %zx @%llx [%llx]", len, start, i_size);

/* The dirty region was entirely beyond the EOF. */
fscache_clear_page_bits(mapping, start, len, caching);
@@ -691,7 +592,8 @@ static ssize_t afs_write_back_from_locked_folio(struct address_space *mapping,
*/
static int afs_writepages_region(struct address_space *mapping,
struct writeback_control *wbc,
- loff_t start, loff_t end, loff_t *_next,
+ unsigned long long start,
+ unsigned long long end, loff_t *_next,
bool max_one_loop)
{
struct folio *folio;
@@ -903,7 +805,6 @@ vm_fault_t afs_page_mkwrite(struct vm_fault *vmf)
struct inode *inode = file_inode(file);
struct afs_vnode *vnode = AFS_FS_I(inode);
struct afs_file *af = file->private_data;
- unsigned long priv;
vm_fault_t ret = VM_FAULT_RETRY;

_enter("{{%llx:%llu}},{%lx}", vnode->fid.vid, vnode->fid.vnode, folio_index(folio));
@@ -927,24 +828,15 @@ vm_fault_t afs_page_mkwrite(struct vm_fault *vmf)
if (folio_lock_killable(folio) < 0)
goto out;

- /* We mustn't change folio->private until writeback is complete as that
- * details the portion of the page we need to write back and we might
- * need to redirty the page if there's a problem.
- */
if (folio_wait_writeback_killable(folio) < 0) {
folio_unlock(folio);
goto out;
}

- priv = afs_folio_dirty(folio, 0, folio_size(folio));
- priv = afs_folio_dirty_mmapped(priv);
- if (folio_test_private(folio)) {
- folio_change_private(folio, (void *)priv);
+ if (folio_test_dirty(folio))
trace_afs_folio_dirty(vnode, tracepoint_string("mkwrite+"), folio);
- } else {
- folio_attach_private(folio, (void *)priv);
+ else
trace_afs_folio_dirty(vnode, tracepoint_string("mkwrite"), folio);
- }
file_update_time(file);

ret = VM_FAULT_LOCKED;
@@ -989,30 +881,26 @@ int afs_launder_folio(struct folio *folio)
struct afs_vnode *vnode = AFS_FS_I(folio_inode(folio));
struct iov_iter iter;
struct bio_vec bv;
- unsigned long priv;
- unsigned int f, t;
+ unsigned long long fend, i_size = vnode->netfs.inode.i_size;
+ size_t len;
int ret = 0;

_enter("{%lx}", folio->index);

- priv = (unsigned long)folio_get_private(folio);
- if (folio_clear_dirty_for_io(folio)) {
- f = 0;
- t = folio_size(folio);
- if (folio_test_private(folio)) {
- f = afs_folio_dirty_from(folio, priv);
- t = afs_folio_dirty_to(folio, priv);
- }
+ if (folio_clear_dirty_for_io(folio) && folio_pos(folio) < i_size) {
+ len = folio_size(folio);
+ fend = folio_pos(folio) + len;
+ if (vnode->netfs.inode.i_size < fend)
+ len = fend - i_size;

- bvec_set_folio(&bv, folio, t - f, f);
- iov_iter_bvec(&iter, ITER_SOURCE, &bv, 1, bv.bv_len);
+ bvec_set_folio(&bv, folio, len, 0);
+ iov_iter_bvec(&iter, WRITE, &bv, 1, len);

trace_afs_folio_dirty(vnode, tracepoint_string("launder"), folio);
- ret = afs_store_data(vnode, &iter, folio_pos(folio) + f, true);
+ ret = afs_store_data(vnode, &iter, folio_pos(folio), true);
}

trace_afs_folio_dirty(vnode, tracepoint_string("laundered"), folio);
- folio_detach_private(folio);
folio_wait_fscache(folio);
return ret;
}
diff --git a/include/trace/events/afs.h b/include/trace/events/afs.h
index 597677acc6b1..08506680350c 100644
--- a/include/trace/events/afs.h
+++ b/include/trace/events/afs.h
@@ -846,26 +846,18 @@ TRACE_EVENT(afs_folio_dirty,
__field(struct afs_vnode *, vnode)
__field(const char *, where)
__field(pgoff_t, index)
- __field(unsigned long, from)
- __field(unsigned long, to)
+ __field(size_t, size)
),

TP_fast_assign(
- unsigned long priv = (unsigned long)folio_get_private(folio);
__entry->vnode = vnode;
__entry->where = where;
__entry->index = folio_index(folio);
- __entry->from = afs_folio_dirty_from(folio, priv);
- __entry->to = afs_folio_dirty_to(folio, priv);
- __entry->to |= (afs_is_folio_dirty_mmapped(priv) ?
- (1UL << (BITS_PER_LONG - 1)) : 0);
+ __entry->size = folio_size(folio);
),

- TP_printk("vn=%p %lx %s %lx-%lx%s",
- __entry->vnode, __entry->index, __entry->where,
- __entry->from,
- __entry->to & ~(1UL << (BITS_PER_LONG - 1)),
- __entry->to & (1UL << (BITS_PER_LONG - 1)) ? " M" : "")
+ TP_printk("vn=%p ix=%05lx s=%05lx %s",
+ __entry->vnode, __entry->index, __entry->size, __entry->where)
);

TRACE_EVENT(afs_call_state,