The patch titled
Subject: fsdax: introduce dax_iomap_cow_copy()
has been added to the -mm mm-unstable branch. Its filename is
fsdax-introduce-dax_iomap_cow_copy.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/fsdax-introduce-dax_iomap_cow_copy.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Shiyang Ruan <ruansy.fnst@xxxxxxxxxxx>
Subject: fsdax: introduce dax_iomap_cow_copy()
Date: Fri, 3 Jun 2022 13:37:33 +0800
In the case where the iomap is a write operation and iomap is not equal to
srcmap after iomap_begin, we consider it is a CoW operation.
In this case, the destination (iomap->addr) points to a newly allocated
extent. It is needed to copy the data from srcmap to the extent. In
theory, it is better to copy the head and tail ranges which is outside of
the non-aligned area instead of copying the whole aligned range. But in
dax page fault, it will always be an aligned range. So copy the whole
range in this case.
Link: https://lkml.kernel.org/r/20220603053738.1218681-10-ruansy.fnst@xxxxxxxxxxx
Signed-off-by: Shiyang Ruan <ruansy.fnst@xxxxxxxxxxx>
Reviewed-by: Christoph Hellwig <hch@xxxxxx>
Reviewed-by: Darrick J. Wong <djwong@xxxxxxxxxx>
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Dan Williams <dan.j.wiliams@xxxxxxxxx>
Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
Cc: Dave Chinner <david@xxxxxxxxxxxxx>
Cc: Goldwyn Rodrigues <rgoldwyn@xxxxxxxx>
Cc: Goldwyn Rodrigues <rgoldwyn@xxxxxxx>
Cc: Jane Chu <jane.chu@xxxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: Miaohe Lin <linmiaohe@xxxxxxxxxx>
Cc: Naoya Horiguchi <naoya.horiguchi@xxxxxxx>
Cc: Ritesh Harjani <riteshh@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
fs/dax.c | 88 +++++++++++++++++++++++++++++++++++++++++++++++++----
1 file changed, 83 insertions(+), 5 deletions(-)
--- a/fs/dax.c~fsdax-introduce-dax_iomap_cow_copy
+++ a/fs/dax.c
@@ -1062,6 +1062,60 @@ out:
return rc;
}
+/**
+ * dax_iomap_cow_copy - Copy the data from source to destination before write
+ * @pos: address to do copy from.
+ * @length: size of copy operation.
+ * @align_size: aligned w.r.t align_size (either PMD_SIZE or PAGE_SIZE)
+ * @srcmap: iomap srcmap
+ * @daddr: destination address to copy to.
+ *
+ * This can be called from two places. Either during DAX write fault (page
+ * aligned), to copy the length size data to daddr. Or, while doing normal DAX
+ * write operation, dax_iomap_actor() might call this to do the copy of either
+ * start or end unaligned address. In the latter case the rest of the copy of
+ * aligned ranges is taken care by dax_iomap_actor() itself.
+ */
+static int dax_iomap_cow_copy(loff_t pos, uint64_t length, size_t align_size,
+ const struct iomap *srcmap, void *daddr)
+{
+ loff_t head_off = pos & (align_size - 1);
+ size_t size = ALIGN(head_off + length, align_size);
+ loff_t end = pos + length;
+ loff_t pg_end = round_up(end, align_size);
+ bool copy_all = head_off == 0 && end == pg_end;
+ void *saddr = 0;
+ int ret = 0;
+
+ ret = dax_iomap_direct_access(srcmap, pos, size, &saddr, NULL);
+ if (ret)
+ return ret;
+
+ if (copy_all) {
+ ret = copy_mc_to_kernel(daddr, saddr, length);
+ return ret ? -EIO : 0;
+ }
+
+ /* Copy the head part of the range */
+ if (head_off) {
+ ret = copy_mc_to_kernel(daddr, saddr, head_off);
+ if (ret)
+ return -EIO;
+ }
+
+ /* Copy the tail part of the range */
+ if (end < pg_end) {
+ loff_t tail_off = head_off + length;
+ loff_t tail_len = pg_end - end;
+
+ ret = copy_mc_to_kernel(daddr + tail_off, saddr + tail_off,
+ tail_len);
+ if (ret)
+ return -EIO;
+ }
+ return 0;
+}
+
/*
* The user has performed a load from a hole in the file. Allocating a new
* page in the file would cause excessive storage usage for workloads with
@@ -1232,15 +1286,17 @@ static loff_t dax_iomap_iter(const struc
struct iov_iter *iter)
{
const struct iomap *iomap = &iomi->iomap;
+ const struct iomap *srcmap = &iomi->srcmap;
loff_t length = iomap_length(iomi);
loff_t pos = iomi->pos;
struct dax_device *dax_dev = iomap->dax_dev;
loff_t end = pos + length, done = 0;
+ bool write = iov_iter_rw(iter) == WRITE;
ssize_t ret = 0;
size_t xfer;
int id;
- if (iov_iter_rw(iter) == READ) {
+ if (!write) {
end = min(end, i_size_read(iomi->inode));
if (pos >= end)
return 0;
@@ -1249,7 +1305,12 @@ static loff_t dax_iomap_iter(const struc
return iov_iter_zero(min(length, end - pos), iter);
}
- if (WARN_ON_ONCE(iomap->type != IOMAP_MAPPED))
+ /*
+ * In DAX mode, enforce either pure overwrites of written extents, or
+ * writes to unwritten extents as part of a copy-on-write operation.
+ */
+ if (WARN_ON_ONCE(iomap->type != IOMAP_MAPPED &&
+ !(iomap->flags & IOMAP_F_SHARED)))
return -EIO;
/*
@@ -1291,6 +1352,14 @@ static loff_t dax_iomap_iter(const struc
break;
}
+ if (write &&
+ srcmap->type != IOMAP_HOLE && srcmap->addr != iomap->addr) {
+ ret = dax_iomap_cow_copy(pos, length, PAGE_SIZE, srcmap,
+ kaddr);
+ if (ret)
+ break;
+ }
+
map_len = PFN_PHYS(map_len);
kaddr += offset;
map_len -= offset;
@@ -1300,7 +1369,7 @@ static loff_t dax_iomap_iter(const struc
if (recovery)
xfer = dax_recovery_write(dax_dev, pgoff, kaddr,
map_len, iter);
- else if (iov_iter_rw(iter) == WRITE)
+ else if (write)
xfer = dax_copy_from_iter(dax_dev, pgoff, kaddr,
map_len, iter);
else
@@ -1440,6 +1509,7 @@ static vm_fault_t dax_fault_iter(struct
{
struct address_space *mapping = vmf->vma->vm_file->f_mapping;
const struct iomap *iomap = &iter->iomap;
+ const struct iomap *srcmap = &iter->srcmap;
size_t size = pmd ? PMD_SIZE : PAGE_SIZE;
loff_t pos = (loff_t)xas->xa_index << PAGE_SHIFT;
bool write = vmf->flags & FAULT_FLAG_WRITE;
@@ -1447,6 +1517,7 @@ static vm_fault_t dax_fault_iter(struct
unsigned long entry_flags = pmd ? DAX_PMD : 0;
int err = 0;
pfn_t pfn;
+ void *kaddr;
if (!pmd && vmf->cow_page)
return dax_fault_cow_page(vmf, iter);
@@ -1459,18 +1530,25 @@ static vm_fault_t dax_fault_iter(struct
return dax_pmd_load_hole(xas, vmf, iomap, entry);
}
- if (iomap->type != IOMAP_MAPPED) {
+ if (iomap->type != IOMAP_MAPPED && !(iomap->flags & IOMAP_F_SHARED)) {
WARN_ON_ONCE(1);
return pmd ? VM_FAULT_FALLBACK : VM_FAULT_SIGBUS;
}
- err = dax_iomap_direct_access(&iter->iomap, pos, size, NULL, &pfn);
+ err = dax_iomap_direct_access(iomap, pos, size, &kaddr, &pfn);
if (err)
return pmd ? VM_FAULT_FALLBACK : dax_fault_return(err);
*entry = dax_insert_entry(xas, mapping, vmf, *entry, pfn, entry_flags,
write && !sync);
+ if (write &&
+ srcmap->type != IOMAP_HOLE && srcmap->addr != iomap->addr) {
+ err = dax_iomap_cow_copy(pos, size, size, srcmap, kaddr);
+ if (err)
+ return dax_fault_return(err);
+ }
+
if (sync)
return dax_fault_synchronous_pfnp(pfnp, pfn);
_
Patches currently in -mm which might be from ruansy.fnst@xxxxxxxxxxx are
dax-introduce-holder-for-dax_device.patch
mm-factor-helpers-for-memory_failure_dev_pagemap.patch
pagemappmem-introduce-memory_failure.patch
fsdax-introduce-dax_lock_mapping_entry.patch
mm-introduce-mf_dax_kill_procs-for-fsdax-case.patch
xfs-implement-notify_failure-for-xfs.patch
fsdax-set-a-cow-flag-when-associate-reflink-mappings.patch
fsdax-output-address-in-dax_iomap_pfn-and-rename-it.patch
fsdax-introduce-dax_iomap_cow_copy.patch
fsdax-replace-mmap-entry-in-case-of-cow.patch
fsdax-add-dax_iomap_cow_copy-for-dax-zero.patch
fsdax-dedup-file-range-to-use-a-compare-function.patch
xfs-support-cow-in-fsdax-mode.patch
xfs-add-dax-dedupe-support.patch
