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Date: Thu, 25 Oct 2012 16:50:45 +0200
From: Miklos Szeredi <miklos@...redi.hu>
To: Maxim Patlasov <mpatlasov@...allels.com>
Cc: fuse-devel@...ts.sourceforge.net, linux-kernel@...r.kernel.org,
devel@...nvz.org
Subject: Re: [PATCH 10/11] fuse: optimize fuse_get_user_pages() - v2
Maxim Patlasov <mpatlasov@...allels.com> writes:
> Let fuse_get_user_pages() pack as many iov-s to a single fuse_req as
> possible. This is very beneficial in case of iov[] consisting of many
> iov-s of relatively small sizes (e.g. PAGE_SIZE).
>
> Changed in v2:
> - renamed local vars in fuse_page_descs_length_init() to be more readable
>
> Signed-off-by: Maxim Patlasov <mpatlasov@...allels.com>
> ---
> fs/fuse/file.c | 94 +++++++++++++++++++++++++++++++++++---------------------
> 1 files changed, 58 insertions(+), 36 deletions(-)
>
> diff --git a/fs/fuse/file.c b/fs/fuse/file.c
> index db9efb5..4d30697 100644
> --- a/fs/fuse/file.c
> +++ b/fs/fuse/file.c
> @@ -1047,13 +1047,24 @@ static void fuse_release_user_pages(struct fuse_req *req, int write)
> }
> }
>
> -static inline void fuse_page_descs_length_init(struct fuse_req *req)
> +static inline void fuse_page_descs_length_init(struct fuse_req *req,
> + unsigned index, int nr_pages)
> {
> - int i;
> + while (nr_pages-- > 0)
Please avoid such constructs. They are hard to read and easy to mess
up.
Use an auxiliary local variable, just like you used to.
> + req->page_descs[index + nr_pages].length = PAGE_SIZE -
> + req->page_descs[index + nr_pages].offset;
> +}
>
> - for (i = 0; i < req->num_pages; i++)
> - req->page_descs[i].length = PAGE_SIZE -
> - req->page_descs[i].offset;
> +static inline unsigned long fuse_get_ua(const struct iovec *iov,
fuse_get_user_addr()
> + size_t iov_offset)
> +{
> + return (unsigned long)iov->iov_base + iov_offset;
> +}
> +
> +static inline size_t fuse_get_fr_sz(const struct iovec *iov, size_t
> iov_offset,
iov_iter_single_seg_count() is the function you are reimplementing here,
I guess.
I haven't reviewed the as I think it will automatically get cleaner if
you switch to iov_iter.
> + size_t max_size)
> +{
> + return min_t(size_t, iov->iov_len - iov_offset, max_size);
> }
>
> static int fuse_get_user_pages(struct fuse_req *req,
> @@ -1062,14 +1073,12 @@ static int fuse_get_user_pages(struct fuse_req *req,
> size_t *iov_offset_p,
> size_t *nbytesp, int write)
> {
> - size_t nbytes = *nbytesp;
> - size_t frag_size = min_t(size_t, nbytes, (*iov_pp)->iov_len - *iov_offset_p);
> - unsigned long user_addr = (unsigned long)(*iov_pp)->iov_base + *iov_offset_p;
> - unsigned offset = user_addr & ~PAGE_MASK;
> - int npages;
> + size_t nbytes = 0; /* # bytes already packed in req */
>
> /* Special case for kernel I/O: can copy directly into the buffer */
> if (segment_eq(get_fs(), KERNEL_DS)) {
> + unsigned long user_addr = fuse_get_ua(*iov_pp, *iov_offset_p);
> +
> if (write)
> req->in.args[1].value = (void *) user_addr;
> else
> @@ -1077,42 +1086,55 @@ static int fuse_get_user_pages(struct fuse_req *req,
>
> (*iov_pp)++;
> (*nr_segs_p)--;
> - *nbytesp = frag_size;
> + *nbytesp = fuse_get_fr_sz(*iov_pp, *iov_offset_p, *nbytesp);
> return 0;
> }
>
> - nbytes = min_t(size_t, frag_size, FUSE_MAX_PAGES_PER_REQ << PAGE_SHIFT);
> - npages = (nbytes + offset + PAGE_SIZE - 1) >> PAGE_SHIFT;
> - npages = clamp(npages, 1, FUSE_MAX_PAGES_PER_REQ);
> - npages = get_user_pages_fast(user_addr, npages, !write, req->pages);
> - if (npages < 0)
> - return npages;
> + while (nbytes < *nbytesp && req->num_pages < FUSE_MAX_PAGES_PER_REQ) {
> + int npages;
> + unsigned long user_addr = fuse_get_ua(*iov_pp, *iov_offset_p);
> + unsigned offset = user_addr & ~PAGE_MASK;
> + size_t frag_size = fuse_get_fr_sz(*iov_pp, *iov_offset_p,
> + *nbytesp - nbytes);
>
> - req->num_pages = npages;
> - req->page_descs[0].offset = offset;
> - fuse_page_descs_length_init(req);
> + int n = FUSE_MAX_PAGES_PER_REQ - req->num_pages;
> + frag_size = min_t(size_t, frag_size, n << PAGE_SHIFT);
>
> - if (write)
> - req->in.argpages = 1;
> - else
> - req->out.argpages = 1;
> + npages = (frag_size + offset + PAGE_SIZE - 1) >> PAGE_SHIFT;
> + npages = clamp(npages, 1, n);
>
> - nbytes = (req->num_pages << PAGE_SHIFT) - req->page_descs[0].offset;
> + npages = get_user_pages_fast(user_addr, npages, !write,
> + &req->pages[req->num_pages]);
> + if (npages < 0)
> + return npages;
>
> - if (frag_size < nbytes)
> - req->page_descs[req->num_pages - 1].length -=
> - nbytes - frag_size;
> + frag_size = min_t(size_t, frag_size,
> + (npages << PAGE_SHIFT) - offset);
> + nbytes += frag_size;
>
> - *nbytesp = min(frag_size, nbytes);
> + if (frag_size < (*iov_pp)->iov_len - *iov_offset_p) {
> + *iov_offset_p += frag_size;
> + } else {
> + (*iov_pp)++;
> + (*nr_segs_p)--;
> + *iov_offset_p = 0;
> + }
>
> - if (*nbytesp < (*iov_pp)->iov_len - *iov_offset_p) {
> - *iov_offset_p += *nbytesp;
> - } else {
> - (*iov_pp)++;
> - (*nr_segs_p)--;
> - *iov_offset_p = 0;
> + req->page_descs[req->num_pages].offset = offset;
> + fuse_page_descs_length_init(req, req->num_pages, npages);
> +
> + req->num_pages += npages;
> + req->page_descs[req->num_pages - 1].length -=
> + (npages << PAGE_SHIFT) - offset - frag_size;
> }
>
> + if (write)
> + req->in.argpages = 1;
> + else
> + req->out.argpages = 1;
> +
> + *nbytesp = nbytes;
> +
> return 0;
> }
>
> @@ -1954,7 +1976,7 @@ long fuse_do_ioctl(struct file *file, unsigned int cmd, unsigned long arg,
> }
> memcpy(req->pages, pages, sizeof(req->pages[0]) * num_pages);
> req->num_pages = num_pages;
> - fuse_page_descs_length_init(req);
> + fuse_page_descs_length_init(req, 0, req->num_pages);
>
> /* okay, let's send it to the client */
> req->in.h.opcode = FUSE_IOCTL;
--
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