lkml.org 
[lkml]   [2021]   [Jul]   [21]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [PATCH v14 054/138] mm: Add kmap_local_folio()
    On Wed, Jul 21, 2021 at 03:12:03PM +0100, Matthew Wilcox wrote:
    > On Wed, Jul 21, 2021 at 12:58:24PM +0300, Mike Rapoport wrote:
    > > > +/**
    > > > + * kmap_local_folio - Map a page in this folio for temporary usage
    > > > + * @folio: The folio to be mapped.
    > > > + * @offset: The byte offset within the folio.
    > > > + *
    > > > + * Returns: The virtual address of the mapping
    > > > + *
    > > > + * Can be invoked from any context.
    > >
    > > Context: Can be invoked from any context.
    > >
    > > > + *
    > > > + * Requires careful handling when nesting multiple mappings because the map
    > > > + * management is stack based. The unmap has to be in the reverse order of
    > > > + * the map operation:
    > > > + *
    > > > + * addr1 = kmap_local_folio(page1, offset1);
    > > > + * addr2 = kmap_local_folio(page2, offset2);
    > >
    > > Please s/page/folio/g here and in the description below
    > >
    > > > + * ...
    > > > + * kunmap_local(addr2);
    > > > + * kunmap_local(addr1);
    > > > + *
    > > > + * Unmapping addr1 before addr2 is invalid and causes malfunction.
    > > > + *
    > > > + * Contrary to kmap() mappings the mapping is only valid in the context of
    > > > + * the caller and cannot be handed to other contexts.
    > > > + *
    > > > + * On CONFIG_HIGHMEM=n kernels and for low memory pages this returns the
    > > > + * virtual address of the direct mapping. Only real highmem pages are
    > > > + * temporarily mapped.
    > > > + *
    > > > + * While it is significantly faster than kmap() for the higmem case it
    > > > + * comes with restrictions about the pointer validity. Only use when really
    > > > + * necessary.
    > > > + *
    > > > + * On HIGHMEM enabled systems mapping a highmem page has the side effect of
    > > > + * disabling migration in order to keep the virtual address stable across
    > > > + * preemption. No caller of kmap_local_folio() can rely on this side effect.
    > > > + */
    >
    > kmap_local_folio() only maps one page from the folio. So it's not
    > appropriate to s/page/folio/g. I fiddled with the description a bit to
    > make this clearer:
    >
    > /**
    > * kmap_local_folio - Map a page in this folio for temporary usage
    > - * @folio: The folio to be mapped.
    > - * @offset: The byte offset within the folio.
    > - *
    > - * Returns: The virtual address of the mapping
    > - *
    > - * Can be invoked from any context.
    > + * @folio: The folio containing the page.
    > + * @offset: The byte offset within the folio which identifies the page.
    > *
    > * Requires careful handling when nesting multiple mappings because the map
    > * management is stack based. The unmap has to be in the reverse order of
    > * the map operation:
    > *
    > - * addr1 = kmap_local_folio(page1, offset1);
    > - * addr2 = kmap_local_folio(page2, offset2);
    > + * addr1 = kmap_local_folio(folio1, offset1);
    > + * addr2 = kmap_local_folio(folio2, offset2);
    > * ...
    > * kunmap_local(addr2);
    > * kunmap_local(addr1);
    > @@ -131,6 +127,9 @@ static inline void *kmap_local_page(struct page *page);
    > * On HIGHMEM enabled systems mapping a highmem page has the side effect of
    > * disabling migration in order to keep the virtual address stable across
    > * preemption. No caller of kmap_local_folio() can rely on this side effect.
    > + *
    > + * Context: Can be invoked from any context.
    > + * Return: The virtual address of @offset.
    > */
    > static inline void *kmap_local_folio(struct folio *folio, size_t offset)

    This is clearer, thanks!

    Maybe just add page to Return: description:

    * Return: The virtual address of page @offset.

    --
    Sincerely yours,
    Mike.

    \
     
     \ /
      Last update: 2021-07-21 16:29    [W:4.111 / U:0.364 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site