Re: [PATCH v14 5/7] btrfs: send: allocate send buffer with alloc_page() and vmap() for v2

[Sweet Tea Dorminy <sweettea-kernel@dorminy.me>]

On 3/17/22 13:25, Omar Sandoval wrote:
> From: Omar Sandoval <osandov@fb.com>
> 
> For encoded writes, we need the raw pages for reading compressed data
> directly via a bio.
Perhaps:
"For encoded writes, the existing btrfs_encoded_read*() functions expect 
a list of raw pages."

I think it would be a better to continue just vmalloc'ing a large 
continuous buffer and translating each page in the buffer into its raw 
page with something like is_vmalloc_addr(data) ? vmalloc_to_page(data) : 
virt_to_page(data). Vmalloc can request a higher-order allocation, which 
probably doesn't matter but might slightly improve memory locality. And 
in terms of readability, I somewhat like the elegance of having a single 
identical kvmalloc call to allocate and send_buf in both cases, even if 
we do need to initialize the page list for some v2 commands.