| Message ID | 20200819184850.24779-3-willy@infradead.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Return head pages from find_get_entry and find_lock_entry | expand |
On Wed, Aug 19, 2020 at 07:48:44PM +0100, Matthew Wilcox (Oracle) wrote: > The current code does not protect against swapoff of the underlying > swap device, so this is a bug fix as well as a worthwhile reduction in > code complexity. > > Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org> > --- > mm/memcontrol.c | 25 ++----------------------- > 1 file changed, 2 insertions(+), 23 deletions(-) > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index b807952b4d43..4075f214a841 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -5539,35 +5539,14 @@ static struct page *mc_handle_swap_pte(struct vm_area_struct *vma, > static struct page *mc_handle_file_pte(struct vm_area_struct *vma, > unsigned long addr, pte_t ptent, swp_entry_t *entry) > { > - struct page *page = NULL; > - struct address_space *mapping; > - pgoff_t pgoff; > - > if (!vma->vm_file) /* anonymous vma */ > return NULL; > if (!(mc.flags & MOVE_FILE)) > return NULL; > > - mapping = vma->vm_file->f_mapping; > - pgoff = linear_page_index(vma, addr); > - > /* page is moved even if it's not RSS of this task(page-faulted). */ > -#ifdef CONFIG_SWAP > - /* shmem/tmpfs may report page out on swap: account for that too. */ > - if (shmem_mapping(mapping)) { > - page = find_get_entry(mapping, pgoff); > - if (xa_is_value(page)) { > - swp_entry_t swp = radix_to_swp_entry(page); > - *entry = swp; > - page = find_get_page(swap_address_space(swp), > - swp_offset(swp)); > - } > - } else > - page = find_get_page(mapping, pgoff); > -#else > - page = find_get_page(mapping, pgoff); > -#endif > - return page; > + return find_get_swap_page(vma->vm_file->f_mapping, > + linear_page_index(vma, addr)); The refactor makes sense to me, but the name is confusing. We're not looking for a swap page, we're primarily looking for a file page in the page cache mapping that's handed in. Only in the special case where it's a shmem mapping and there is a swap entry do we consult the auxiliary swap cache. How about find_get_page_or_swapcache()? find_get_page_shmemswap()? Maybe you have a better idea. It's a fairly specialized operation that isn't widely used, so a longer name isn't a bad thing IMO.
On Wed, Aug 26, 2020 at 10:20:02AM -0400, Johannes Weiner wrote: > On Wed, Aug 19, 2020 at 07:48:44PM +0100, Matthew Wilcox (Oracle) wrote: > > + return find_get_swap_page(vma->vm_file->f_mapping, > > + linear_page_index(vma, addr)); > > The refactor makes sense to me, but the name is confusing. We're not > looking for a swap page, we're primarily looking for a file page in > the page cache mapping that's handed in. Only in the special case > where it's a shmem mapping and there is a swap entry do we consult the > auxiliary swap cache. > > How about find_get_page_or_swapcache()? find_get_page_shmemswap()? > Maybe you have a better idea. It's a fairly specialized operation that > isn't widely used, so a longer name isn't a bad thing IMO. Yeah, I had trouble with the naming here too. get_page_even_from_swap() find_get_shmem_page() or maybe refactor the whole thing: struct page *page = find_get_entry(mapping, index); page = find_swap_page(mapping, page); struct page *find_swap_page(struct address_space *mapping, struct page *page) { swp_entry_t swp; struct swap_info_struct *si; if (!xa_is_value(page)) return page; if (!shmem_mapping(mapping)) return NULL; ... }
On Wed, Aug 26, 2020 at 03:54:14PM +0100, Matthew Wilcox wrote: > On Wed, Aug 26, 2020 at 10:20:02AM -0400, Johannes Weiner wrote: > > On Wed, Aug 19, 2020 at 07:48:44PM +0100, Matthew Wilcox (Oracle) wrote: > > > + return find_get_swap_page(vma->vm_file->f_mapping, > > > + linear_page_index(vma, addr)); > > > > The refactor makes sense to me, but the name is confusing. We're not > > looking for a swap page, we're primarily looking for a file page in > > the page cache mapping that's handed in. Only in the special case > > where it's a shmem mapping and there is a swap entry do we consult the > > auxiliary swap cache. > > > > How about find_get_page_or_swapcache()? find_get_page_shmemswap()? > > Maybe you have a better idea. It's a fairly specialized operation that > > isn't widely used, so a longer name isn't a bad thing IMO. > > Yeah, I had trouble with the naming here too. > > get_page_even_from_swap() > find_get_shmem_page() > > or maybe refactor the whole thing: > > struct page *page = find_get_entry(mapping, index); > page = find_swap_page(mapping, page); > > struct page *find_swap_page(struct address_space *mapping, struct page *page) > { > swp_entry_t swp; > struct swap_info_struct *si; > > if (!xa_is_value(page)) > return page; > if (!shmem_mapping(mapping)) > return NULL; > > ... > } Yeah, I like the idea of two lookups if we can't find a good name for the operation that combines them. I'd just bubble the control flow that links them up to the callsite - that still seems plenty compact for two callsites, and keeps all the shmem magic in shmem code: page = find_get_entry(mapping, index); if (xa_is_value(page)) if (shmem_mapping(mapping)) page = lookup_shmem_swap_cache(page); else page = NULL; So close to making radix_to_swp_entry() & co. private to shmem.c, too - if it weren't for force_shm_swapin_readahead(). Ah well.
On Wed, Aug 26, 2020 at 10:20:02AM -0400, Johannes Weiner wrote: > The refactor makes sense to me, but the name is confusing. We're not > looking for a swap page, we're primarily looking for a file page in > the page cache mapping that's handed in. Only in the special case > where it's a shmem mapping and there is a swap entry do we consult the > auxiliary swap cache. > > How about find_get_page_or_swapcache()? find_get_page_shmemswap()? > Maybe you have a better idea. It's a fairly specialized operation that > isn't widely used, so a longer name isn't a bad thing IMO. Got it. find_get_incore_page(). I was going to go with inmem, but that it matches mincore sold me on it. /** * find_get_incore_page - Find and get a page from the page or swap caches. * @mapping: The address_space to search. * @index: The page cache index. * * This differs from find_get_page() in that it will also look for the * page in the swap cache. * * Return: The found page or %NULL. */ I was focusing too much on what the function did, not why it was doing it.
On Thu, Aug 27, 2020 at 01:59:41PM +0100, Matthew Wilcox wrote: > On Wed, Aug 26, 2020 at 10:20:02AM -0400, Johannes Weiner wrote: > > The refactor makes sense to me, but the name is confusing. We're not > > looking for a swap page, we're primarily looking for a file page in > > the page cache mapping that's handed in. Only in the special case > > where it's a shmem mapping and there is a swap entry do we consult the > > auxiliary swap cache. > > > > How about find_get_page_or_swapcache()? find_get_page_shmemswap()? > > Maybe you have a better idea. It's a fairly specialized operation that > > isn't widely used, so a longer name isn't a bad thing IMO. > > Got it. find_get_incore_page(). I was going to go with inmem, but that > it matches mincore sold me on it. > > /** > * find_get_incore_page - Find and get a page from the page or swap caches. > * @mapping: The address_space to search. > * @index: The page cache index. > * > * This differs from find_get_page() in that it will also look for the > * page in the swap cache. > * > * Return: The found page or %NULL. > */ Nice work, that's perfect. > I was focusing too much on what the function did, not why it was doing it. Me too.
diff --git a/mm/memcontrol.c b/mm/memcontrol.c index b807952b4d43..4075f214a841 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -5539,35 +5539,14 @@ static struct page *mc_handle_swap_pte(struct vm_area_struct *vma, static struct page *mc_handle_file_pte(struct vm_area_struct *vma, unsigned long addr, pte_t ptent, swp_entry_t *entry) { - struct page *page = NULL; - struct address_space *mapping; - pgoff_t pgoff; - if (!vma->vm_file) /* anonymous vma */ return NULL; if (!(mc.flags & MOVE_FILE)) return NULL; - mapping = vma->vm_file->f_mapping; - pgoff = linear_page_index(vma, addr); - /* page is moved even if it's not RSS of this task(page-faulted). */ -#ifdef CONFIG_SWAP - /* shmem/tmpfs may report page out on swap: account for that too. */ - if (shmem_mapping(mapping)) { - page = find_get_entry(mapping, pgoff); - if (xa_is_value(page)) { - swp_entry_t swp = radix_to_swp_entry(page); - *entry = swp; - page = find_get_page(swap_address_space(swp), - swp_offset(swp)); - } - } else - page = find_get_page(mapping, pgoff); -#else - page = find_get_page(mapping, pgoff); -#endif - return page; + return find_get_swap_page(vma->vm_file->f_mapping, + linear_page_index(vma, addr)); } /**
The current code does not protect against swapoff of the underlying swap device, so this is a bug fix as well as a worthwhile reduction in code complexity. Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org> --- mm/memcontrol.c | 25 ++----------------------- 1 file changed, 2 insertions(+), 23 deletions(-)