netfs: Speed up buffered reading

Improve the efficiency of buffered reads in a number of ways:

(1) Overhaul the algorithm in general so that it's a lot more compact and
split the read submiss

netfs: Speed up buffered reading

Improve the efficiency of buffered reads in a number of ways:

(1) Overhaul the algorithm in general so that it's a lot more compact and
split the read submission code between buffered and unbuffered
versions. The unbuffered version can be vastly simplified.

(2) Read-result collection is handed off to a work queue rather than being
done in the I/O thread. Multiple subrequests can be processes
simultaneously.

(3) When a subrequest is collected, any folios it fully spans are
collected and "spare" data on either side is donated to either the
previous or the next subrequest in the sequence.

Notes:

(*) Readahead expansion is massively slows down fio, presumably because it
causes a load of extra allocations, both folio and xarray, up front
before RPC requests can be transmitted.

(*) RDMA with cifs does appear to work, both with SIW and RXE.

(*) PG_private_2-based reading and copy-to-cache is split out into its own
file and altered to use folio_queue. Note that the copy to the cache
now creates a new write transaction against the cache and adds the
folios to be copied into it. This allows it to use part of the
writeback I/O code.

Signed-off-by: David Howells <[email protected]>
cc: Jeff Layton <[email protected]>
cc: [email protected]
cc: [email protected]
Link: https://lore.kernel.org/r/[email protected]/ # v2
Signed-off-by: Christian Brauner <[email protected]>

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netfs: Add func to calculate pagecount/size-limited span of an iterator

Add a function to work out how much of an ITER_BVEC or ITER_XARRAY iterator
we can use in a pagecount-limited and size-limited

netfs: Add func to calculate pagecount/size-limited span of an iterator

Add a function to work out how much of an ITER_BVEC or ITER_XARRAY iterator
we can use in a pagecount-limited and size-limited span. This will be
used, for example, to limit the number of segments in a subrequest to the
maximum number of elements that an RDMA transfer can handle.

Signed-off-by: David Howells <[email protected]>
Reviewed-by: Jeff Layton <[email protected]>
cc: [email protected]
cc: [email protected]
cc: [email protected]

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Move netfs_extract_iter_to_sg() to lib/scatterlist.c

Move netfs_extract_iter_to_sg() to lib/scatterlist.c as it's going to be
used by more than just network filesystems (AF_ALG, for example).

Signe

Move netfs_extract_iter_to_sg() to lib/scatterlist.c

Move netfs_extract_iter_to_sg() to lib/scatterlist.c as it's going to be
used by more than just network filesystems (AF_ALG, for example).

Signed-off-by: David Howells <[email protected]>
cc: Jeff Layton <[email protected]>
cc: Steve French <[email protected]>
cc: Shyam Prasad N <[email protected]>
cc: Rohith Surabattula <[email protected]>
cc: Jens Axboe <[email protected]>
cc: Herbert Xu <[email protected]>
cc: "David S. Miller" <[email protected]>
cc: Eric Dumazet <[email protected]>
cc: Jakub Kicinski <[email protected]>
cc: Paolo Abeni <[email protected]>
cc: Matthew Wilcox <[email protected]>
cc: [email protected]
cc: [email protected]
cc: [email protected]
cc: [email protected]
cc: [email protected]
Signed-off-by: Paolo Abeni <[email protected]>

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Wrap lines at 80

Wrap a line at 80 to stop checkpatch complaining.

Signed-off-by: David Howells <[email protected]>
cc: Jeff Layton <[email protected]>
cc: Steve French <[email protected]>
cc: S

Wrap lines at 80

Wrap a line at 80 to stop checkpatch complaining.

Signed-off-by: David Howells <[email protected]>
cc: Jeff Layton <[email protected]>
cc: Steve French <[email protected]>
cc: Shyam Prasad N <[email protected]>
cc: Rohith Surabattula <[email protected]>
cc: Jens Axboe <[email protected]>
cc: Herbert Xu <[email protected]>
cc: "David S. Miller" <[email protected]>
cc: Eric Dumazet <[email protected]>
cc: Jakub Kicinski <[email protected]>
cc: Paolo Abeni <[email protected]>
cc: Matthew Wilcox <[email protected]>
cc: Simon Horman <[email protected]>
cc: [email protected]
cc: [email protected]
cc: [email protected]
cc: [email protected]
cc: [email protected]
Signed-off-by: Paolo Abeni <[email protected]>

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Fix a couple of spelling mistakes

Fix a couple of spelling mistakes in a comment.

Suggested-by: Simon Horman <[email protected]>
Link: https://lore.kernel.org/r/[email protected]

Fix a couple of spelling mistakes

Fix a couple of spelling mistakes in a comment.

Suggested-by: Simon Horman <[email protected]>
Link: https://lore.kernel.org/r/[email protected]/
Link: https://lore.kernel.org/r/[email protected]/
Signed-off-by: David Howells <[email protected]>
Reviewed-by: Simon Horman <[email protected]>
cc: Jeff Layton <[email protected]>
cc: Steve French <[email protected]>
cc: Shyam Prasad N <[email protected]>
cc: Rohith Surabattula <[email protected]>
cc: Jens Axboe <[email protected]>
cc: Herbert Xu <[email protected]>
cc: "David S. Miller" <[email protected]>
cc: Eric Dumazet <[email protected]>
cc: Jakub Kicinski <[email protected]>
cc: Paolo Abeni <[email protected]>
cc: Matthew Wilcox <[email protected]>
cc: [email protected]
cc: [email protected]
cc: [email protected]
cc: [email protected]
cc: [email protected]
Signed-off-by: Paolo Abeni <[email protected]>

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Drop the netfs_ prefix from netfs_extract_iter_to_sg()

Rename netfs_extract_iter_to_sg() and its auxiliary functions to drop the
netfs_ prefix.

Signed-off-by: David Howells <[email protected]>
cc

Drop the netfs_ prefix from netfs_extract_iter_to_sg()

Rename netfs_extract_iter_to_sg() and its auxiliary functions to drop the
netfs_ prefix.

Signed-off-by: David Howells <[email protected]>
cc: Jeff Layton <[email protected]>
cc: Steve French <[email protected]>
cc: Shyam Prasad N <[email protected]>
cc: Rohith Surabattula <[email protected]>
cc: Jens Axboe <[email protected]>
cc: Herbert Xu <[email protected]>
cc: "Matthew Wilcox (Oracle)" <[email protected]>
cc: "David S. Miller" <[email protected]>
cc: Eric Dumazet <[email protected]>
cc: Jakub Kicinski <[email protected]>
cc: Paolo Abeni <[email protected]>
cc: [email protected]
cc: [email protected]
cc: [email protected]
cc: [email protected]
cc: [email protected]
Signed-off-by: Paolo Abeni <[email protected]>

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netfs: Pass a pointer to virt_to_page()

Like the other calls in this function virt_to_page() expects
a pointer, not an integer.

However since many architectures implement virt_to_pfn() as
a macro,

netfs: Pass a pointer to virt_to_page()

Like the other calls in this function virt_to_page() expects
a pointer, not an integer.

However since many architectures implement virt_to_pfn() as
a macro, this function becomes polymorphic and accepts both a
(unsigned long) and a (void *).

Fix this up with an explicit cast.

Signed-off-by: Linus Walleij <[email protected]>

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netfs: Fix netfs_extract_iter_to_sg() for ITER_UBUF/IOVEC

Fix netfs_extract_iter_to_sg() for ITER_UBUF and ITER_IOVEC to set the
size of the page to the part of the page extracted, not the remaining

netfs: Fix netfs_extract_iter_to_sg() for ITER_UBUF/IOVEC

Fix netfs_extract_iter_to_sg() for ITER_UBUF and ITER_IOVEC to set the
size of the page to the part of the page extracted, not the remaining
amount of data in the extracted page array at that point.

This doesn't yet affect anything as cifs, the only current user, only
passes in non-user-backed iterators.

Fixes: 018584697533 ("netfs: Add a function to extract an iterator into a scatterlist")
Signed-off-by: David Howells <[email protected]>
Reviewed-by: Jeff Layton <[email protected]>
Cc: Steve French <[email protected]>
Cc: Shyam Prasad N <[email protected]>
Cc: Rohith Surabattula <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

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iov: Fix netfs_extract_user_to_sg()

Fix the loop check in netfs_extract_user_to_sg() for extraction from
user-backed iterators to do the body if npages > 0, not if npages < 0
(which it can never be)

iov: Fix netfs_extract_user_to_sg()

Fix the loop check in netfs_extract_user_to_sg() for extraction from
user-backed iterators to do the body if npages > 0, not if npages < 0
(which it can never be).

This isn't currently used by cifs, which only ever extracts data from BVEC,
KVEC and XARRAY iterators at this level, user-backed iterators having being
decanted into BVEC iterators at a higher level to accommodate the work
being done in a kernel thread.

Found by smatch:
fs/netfs/iterator.c:139 netfs_extract_user_to_sg() warn: unsigned 'npages' is never less than zero.

Fixes: 018584697533 ("netfs: Add a function to extract an iterator into a scatterlist")
Reported-by: kernel test robot <[email protected]>
Link: https://lore.kernel.org/oe-kbuild-all/[email protected]/
Reported-by: Dan Carpenter <[email protected]>
Link: https://lore.kernel.org/r/Y/yYnAhoAYDBKixX@kili
Reviewed-by: Paulo Alcantara (SUSE) <[email protected]>
Signed-off-by: David Howells <[email protected]>
cc: Jeff Layton <[email protected]>
cc: [email protected]
cc: [email protected]
Signed-off-by: Steve French <[email protected]>

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netfs: Add a function to extract an iterator into a scatterlist

Provide a function for filling in a scatterlist from the list of pages
contained in an iterator.

If the iterator is UBUF- or IOBUF-ty

netfs: Add a function to extract an iterator into a scatterlist

Provide a function for filling in a scatterlist from the list of pages
contained in an iterator.

If the iterator is UBUF- or IOBUF-type, the pages have a pin taken on them
(as FOLL_PIN).

If the iterator is BVEC-, KVEC- or XARRAY-type, no pin is taken on the
pages and it is left to the caller to manage their lifetime. It cannot be
assumed that a ref can be validly taken, particularly in the case of a KVEC
iterator.

Signed-off-by: David Howells <[email protected]>
cc: Jeff Layton <[email protected]>
cc: Steve French <[email protected]>
cc: Shyam Prasad N <[email protected]>
cc: Rohith Surabattula <[email protected]>
cc: [email protected]
cc: [email protected]
cc: [email protected]
Signed-off-by: Steve French <[email protected]>

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netfs: Add a function to extract a UBUF or IOVEC into a BVEC iterator

Add a function to extract the pages from a user-space supplied iterator
(UBUF- or IOVEC-type) into a BVEC-type iterator, retaini

netfs: Add a function to extract a UBUF or IOVEC into a BVEC iterator

Add a function to extract the pages from a user-space supplied iterator
(UBUF- or IOVEC-type) into a BVEC-type iterator, retaining the pages by
getting a pin on them (as FOLL_PIN) as we go.

This is useful in three situations:

(1) A userspace thread may have a sibling that unmaps or remaps the
process's VM during the operation, changing the assignment of the
pages and potentially causing an error. Retaining the pages keeps
some pages around, even if this occurs; futher, we find out at the
point of extraction if EFAULT is going to be incurred.

(2) Pages might get swapped out/discarded if not retained, so we want to
retain them to avoid the reload causing a deadlock due to a DIO
from/to an mmapped region on the same file.

(3) The iterator may get passed to sendmsg() by the filesystem. If a
fault occurs, we may get a short write to a TCP stream that's then
tricky to recover from.

We don't deal with other types of iterator here, leaving it to other
mechanisms to retain the pages (eg. PG_locked, PG_writeback and the pipe
lock).

Signed-off-by: David Howells <[email protected]>
cc: Jeff Layton <[email protected]>
cc: Steve French <[email protected]>
cc: Shyam Prasad N <[email protected]>
cc: Rohith Surabattula <[email protected]>
cc: [email protected]
cc: [email protected]
cc: [email protected]
Signed-off-by: Steve French <[email protected]>

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