Messages in this thread | | | From | Linus Torvalds <> | Date | Mon, 22 May 2023 10:42:12 -0700 | Subject | Re: [PATCH v20 23/32] splice: Convert trace/seq to use direct_splice_read() |
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On Mon, May 22, 2023 at 7:50 AM David Howells <dhowells@redhat.com> wrote: > > We could implement seq_splice_read(). What we would need to do is to change > how the seq buffer is allocated: bulk allocate a bunch of arbitrary pages > which we then vmap(). When we need to splice, we read into the buffer, do a > vunmap() and then splice the pages holding the data we used into the pipe.
Please don't use vmap as a way to do zero-copy.
The virtual mapping games are more expensive than a small copy from some random seq file.
Yes, yes, seq_file currently uses "kvmalloc()", which does fall back to vmalloc too. But the keyword there is "falls back". Most of the time it's just a regular boring kmalloc, and most of the time a seq-file is tiny.
Linus
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