[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [PATCH v2] xen: Convert kmap() to kmap_local_page()
On Wed, 20 Apr 2022, Fabio M. De Francesco wrote: > On mercoledì 20 aprile 2022 15:40:10 CEST Julia Lawall wrote: > > > > On Wed, 20 Apr 2022, Fabio M. De Francesco wrote: > > > > > On mercoledì 20 aprile 2022 08:03:05 CEST Julia Lawall wrote: > > > > > > > > On Wed, 20 Apr 2022, Alaa Mohamed wrote: > > > > > > > > > kmap() is being deprecated and these usages are all local to the > thread > > > > > so there is no reason kmap_local_page() can't be used. > > > > > > > > > > Replace kmap() calls with kmap_local_page(). > > > > > > > > OK, so from a Coccinelle point of view, could we do > > > > > > > > @@ > > > > expression e1,e2,x,f; > > > > @@ > > > > > > > > e1 = > > > > - kmap > > > > + kmap_local_page > > > > (e2) > > > > ... when != x = e1 // not stored in any location and not passed to > > > another function > > > > when != f(...,e1,...) > > > > when != x = e2 > > > > when != f(...,e2,...) > > > > -kunmap(e2) > > > > +kunmap_local(e1) > > > > > > > > julia > > > > > > > > > > I've never spent sufficient time to understand properly the syntax and > > > semantics of expressions of Coccinelle. However, thanks Julia, this > code > > > looks good and can be very helpful. > > > > > > Only a minor objection... it doesn't tell when 'e2' has been allocated > > > within the same function where the kmap() call is. > > > > > > In the particular case that I cite above, I'd prefer to remove the > > > allocation of the page (say with alloc_page()) and convert kmap() / > kunmap() > > > to use kmalloc() / kfree(). > > > > > > Fox example, this is done in the following patch: > > > > > > commit 633b0616cfe0 ("x86/sgx: Remove unnecessary kmap() from > > > sgx_ioc_enclave_init()") from Ira Weiny. > > > > > > Can Coccinelle catch also those special cases where a page that is > passed > > > to kmap() is allocated within that same function (vs. being passed as > > > argument to this function) and, if so, propose a replacement with > > > kmalloc()? > > > > It looks complex in this case, because the allocation is in another > > function, and it is passed to another function. > > This is not the special case I was talking about. In this case your code > for Coccinelle tells the right proposal and it is exactly what Alaa did in > her patch (which is good!). > > I'm talking about other special cases like the one I pointed to with the > link I provided. I'm sorry if my bad English made you think that Alaa's > patch was one of those cases where the page is allocated within the same > function where kmap() is. > > I hope that now I've been clearer :) Ah, sorry for the misunderstanding. If you have an example, I can take a look and propose something for this special case. julia
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