| Message ID | 20210830141051.64090-7-linmiaohe@huawei.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | Cleanups and fixup for page_alloc | expand |
On Mon, Aug 30, 2021 at 10:10:51PM +0800, Miaohe Lin wrote: > Don't use with __GFP_HIGHMEM because page_address() cannot represent > highmem pages without kmap(). Newly allocated pages would leak as > page_address() will return NULL for highmem pages here. But It works > now because the only caller does not specify __GFP_HIGHMEM now. This is a misunderstanding of how alloc_pages_exact() / alloc_pages_exact_nid() work. You simply can't call them with GFP_HIGHMEM. If you really must change anything here, s/__GFP_COMP/(__GFP_COMP|__GFP_HIGHMEM)/g throughout both alloc_pages_exact() and alloc_pages_exact_nid().
On 2021/8/30 22:24, Matthew Wilcox wrote: > On Mon, Aug 30, 2021 at 10:10:51PM +0800, Miaohe Lin wrote: >> Don't use with __GFP_HIGHMEM because page_address() cannot represent >> highmem pages without kmap(). Newly allocated pages would leak as >> page_address() will return NULL for highmem pages here. But It works >> now because the only caller does not specify __GFP_HIGHMEM now. > > This is a misunderstanding of how alloc_pages_exact() / > alloc_pages_exact_nid() work. You simply can't call them with > GFP_HIGHMEM. > Yep, they can't work with GFP_HIGHMEM. So IMO it might be better to get rid of GFP_HIGHMEM explicitly or add a comment to clarify this situation to avoid future misbehavior. But this may be a unnecessary worry... Do you prefer to not change anything here? Many thanks. > If you really must change anything here, > s/__GFP_COMP/(__GFP_COMP|__GFP_HIGHMEM)/g throughout both > alloc_pages_exact() and alloc_pages_exact_nid(). > . >
On 8/31/21 03:56, Miaohe Lin wrote: > On 2021/8/30 22:24, Matthew Wilcox wrote: >> On Mon, Aug 30, 2021 at 10:10:51PM +0800, Miaohe Lin wrote: >>> Don't use with __GFP_HIGHMEM because page_address() cannot represent >>> highmem pages without kmap(). Newly allocated pages would leak as >>> page_address() will return NULL for highmem pages here. But It works >>> now because the only caller does not specify __GFP_HIGHMEM now. >> >> This is a misunderstanding of how alloc_pages_exact() / >> alloc_pages_exact_nid() work. You simply can't call them with >> GFP_HIGHMEM. >> > > Yep, they can't work with GFP_HIGHMEM. So IMO it might be better to > get rid of GFP_HIGHMEM explicitly or add a comment to clarify this > situation to avoid future misbehavior. But this may be a unnecessary > worry... Do you prefer to not change anything here? I agree with the suggestion below... > Many thanks. > >> If you really must change anything here, >> s/__GFP_COMP/(__GFP_COMP|__GFP_HIGHMEM)/g throughout both >> alloc_pages_exact() and alloc_pages_exact_nid(). ... which means __GFP_HIGHMEM would be stripped and additionally there would be a warning.
On 2021/9/1 0:37, Vlastimil Babka wrote: > On 8/31/21 03:56, Miaohe Lin wrote: >> On 2021/8/30 22:24, Matthew Wilcox wrote: >>> On Mon, Aug 30, 2021 at 10:10:51PM +0800, Miaohe Lin wrote: >>>> Don't use with __GFP_HIGHMEM because page_address() cannot represent >>>> highmem pages without kmap(). Newly allocated pages would leak as >>>> page_address() will return NULL for highmem pages here. But It works >>>> now because the only caller does not specify __GFP_HIGHMEM now. >>> >>> This is a misunderstanding of how alloc_pages_exact() / >>> alloc_pages_exact_nid() work. You simply can't call them with >>> GFP_HIGHMEM. >>> >> >> Yep, they can't work with GFP_HIGHMEM. So IMO it might be better to >> get rid of GFP_HIGHMEM explicitly or add a comment to clarify this >> situation to avoid future misbehavior. But this may be a unnecessary >> worry... Do you prefer to not change anything here? > > I agree with the suggestion below... > >> Many thanks. >> >>> If you really must change anything here, >>> s/__GFP_COMP/(__GFP_COMP|__GFP_HIGHMEM)/g throughout both >>> alloc_pages_exact() and alloc_pages_exact_nid(). > > ... which means __GFP_HIGHMEM would be stripped and additionally there would > be a warning. > Looks good for me. Will do. Many thanks! > . >
diff --git a/mm/page_alloc.c b/mm/page_alloc.c index d87b7e6e9e6b..858fd45ecaea 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -5639,7 +5639,7 @@ void * __meminit alloc_pages_exact_nid(int nid, size_t size, gfp_t gfp_mask) if (WARN_ON_ONCE(gfp_mask & __GFP_COMP)) gfp_mask &= ~__GFP_COMP; - p = alloc_pages_node(nid, gfp_mask, order); + p = alloc_pages_node(nid, gfp_mask & ~__GFP_HIGHMEM, order); if (!p) return NULL; return make_alloc_exact((unsigned long)page_address(p), order, size);
Don't use with __GFP_HIGHMEM because page_address() cannot represent highmem pages without kmap(). Newly allocated pages would leak as page_address() will return NULL for highmem pages here. But It works now because the only caller does not specify __GFP_HIGHMEM now. Signed-off-by: Miaohe Lin <linmiaohe@huawei.com> --- mm/page_alloc.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)