Re: [PATCH] mm: get rid of radix tree gfp mask for pagecache_get_page (was: Re: How to handle TIF_MEMDIE stalls?)

Michal Hocko
2014-12-30T13:42:34Z

Andrew,
I've noticed you have taken the patch to mm tree already. I have
realized I haven't marked it for stable which is worth it IMO because
debugging nasty reclaim recursion bugs is definitely a pain and might
fix one and even if it doesn't it is rather straightforward and
shouldn't break anything. So if nobody has anything against I would mark
this for stable 3.16+ AFAICS.

On Mon 29-12-14 20:33:12, Michal Hocko wrote:
> From 3242f56ae8886a3c605d93960e77176dfe1dff43 Mon Sep 17 00:00:00 2001
> From: Michal Hocko <mhocko@suse.cz>
> Date: Mon, 29 Dec 2014 20:30:35 +0100
> Subject: [PATCH] mm: get rid of radix tree gfp mask for pagecache_get_page
>
> 2457aec63745 (mm: non-atomically mark page accessed during page cache
> allocation where possible) has added a separate parameter for specifying
> gfp mask for radix tree allocations.
>
> Not only this is less than optimal from the API point of view
> because it is error prone, it is also buggy currently because
> grab_cache_page_write_begin is using GFP_KERNEL for radix tree and
> if fgp_flags doesn't contain FGP_NOFS (mostly controlled by fs by
> AOP_FLAG_NOFS flag) but the mapping_gfp_mask has __GFP_FS cleared then
> the radix tree allocation wouldn't obey the restriction and might
> recurse into filesystem and cause deadlocks. This is the case for
> most filesystems unfortunately because only ext4 and gfs2 are using
> AOP_FLAG_NOFS.
>
> Let's simply remove radix_gfp_mask parameter because the allocation
> context is same for both page cache and for the radix tree. Just make
> sure that the radix tree gets only the sane subset of the mask (e.g. do
> not pass __GFP_WRITE).
>
> Long term it is more preferable to convert remaining users of
> AOP_FLAG_NOFS to use mapping_gfp_mask instead and simplify this
> interface even further.
>
> Reported-by: Dave Chinner <david@fromorbit.com>
> Signed-off-by: Michal Hocko <mhocko@suse.cz>
> ---
> include/linux/pagemap.h | 13 ++++++-------
> mm/filemap.c | 29 ++++++++++++-----------------
> 2 files changed, 18 insertions(+), 24 deletions(-)
>
> diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
> index 7ea069cd3257..4b3736f7065c 100644
> --- a/include/linux/pagemap.h
> +++ b/include/linux/pagemap.h
> @@ -251,7 +251,7 @@ pgoff_t page_cache_prev_hole(struct address_space *mapping,
> #define FGP_NOWAIT 0x00000020
>
> struct page *pagecache_get_page(struct address_space *mapping, pgoff_t offset,
> - int fgp_flags, gfp_t cache_gfp_mask, gfp_t radix_gfp_mask);
> + int fgp_flags, gfp_t cache_gfp_mask);
>
> /**
> * find_get_page - find and get a page reference
> @@ -266,13 +266,13 @@ struct page *pagecache_get_page(struct address_space *mapping, pgoff_t offset,
> static inline struct page *find_get_page(struct address_space *mapping,
> pgoff_t offset)
> {
> - return pagecache_get_page(mapping, offset, 0, 0, 0);
> + return pagecache_get_page(mapping, offset, 0, 0);
> }
>
> static inline struct page *find_get_page_flags(struct address_space *mapping,
> pgoff_t offset, int fgp_flags)
> {
> - return pagecache_get_page(mapping, offset, fgp_flags, 0, 0);
> + return pagecache_get_page(mapping, offset, fgp_flags, 0);
> }
>
> /**
> @@ -292,7 +292,7 @@ static inline struct page *find_get_page_flags(struct address_space *mapping,
> static inline struct page *find_lock_page(struct address_space *mapping,
> pgoff_t offset)
> {
> - return pagecache_get_page(mapping, offset, FGP_LOCK, 0, 0);
> + return pagecache_get_page(mapping, offset, FGP_LOCK, 0);
> }
>
> /**
> @@ -319,7 +319,7 @@ static inline struct page *find_or_create_page(struct address_space *mapping,
> {
> return pagecache_get_page(mapping, offset,
> FGP_LOCK|FGP_ACCESSED|FGP_CREAT,
> - gfp_mask, gfp_mask & GFP_RECLAIM_MASK);
> + gfp_mask);
> }
>
> /**
> @@ -340,8 +340,7 @@ static inline struct page *grab_cache_page_nowait(struct address_space *mapping,
> {
> return pagecache_get_page(mapping, index,
> FGP_LOCK|FGP_CREAT|FGP_NOFS|FGP_NOWAIT,
> - mapping_gfp_mask(mapping),
> - GFP_NOFS);
> + mapping_gfp_mask(mapping));
> }
>
> struct page *find_get_entry(struct address_space *mapping, pgoff_t offset);
> diff --git a/mm/filemap.c b/mm/filemap.c
> index e8905bc3cbd7..11477d3b7838 100644
> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -1046,8 +1046,7 @@ EXPORT_SYMBOL(find_lock_entry);
> * @mapping: the address_space to search
> * @offset: the page index
> * @fgp_flags: PCG flags
> - * @cache_gfp_mask: gfp mask to use for the page cache data page allocation
> - * @radix_gfp_mask: gfp mask to use for radix tree node allocation
> + * @gfp_mask: gfp mask to use for the page cache data page allocation
> *
> * Looks up the page cache slot at @mapping & @offset.
> *
> @@ -1056,11 +1055,9 @@ EXPORT_SYMBOL(find_lock_entry);
> * FGP_ACCESSED: the page will be marked accessed
> * FGP_LOCK: Page is return locked
> * FGP_CREAT: If page is not present then a new page is allocated using
> - * @cache_gfp_mask and added to the page cache and the VM's LRU
> - * list. If radix tree nodes are allocated during page cache
> - * insertion then @radix_gfp_mask is used. The page is returned
> - * locked and with an increased refcount. Otherwise, %NULL is
> - * returned.
> + * @gfp_mask and added to the page cache and the VM's LRU
> + * list. The page is returned locked and with an increased
> + * refcount. Otherwise, %NULL is returned.
> *
> * If FGP_LOCK or FGP_CREAT are specified then the function may sleep even
> * if the GFP flags specified for FGP_CREAT are atomic.
> @@ -1068,7 +1065,7 @@ EXPORT_SYMBOL(find_lock_entry);
> * If there is a page cache page, it is returned with an increased refcount.
> */
> struct page *pagecache_get_page(struct address_space *mapping, pgoff_t offset,
> - int fgp_flags, gfp_t cache_gfp_mask, gfp_t radix_gfp_mask)
> + int fgp_flags, gfp_t gfp_mask)
> {
> struct page *page;
>
> @@ -1105,13 +1102,11 @@ no_page:
> if (!page && (fgp_flags & FGP_CREAT)) {
> int err;
> if ((fgp_flags & FGP_WRITE) && mapping_cap_account_dirty(mapping))
> - cache_gfp_mask |= __GFP_WRITE;
> - if (fgp_flags & FGP_NOFS) {
> - cache_gfp_mask &= ~__GFP_FS;
> - radix_gfp_mask &= ~__GFP_FS;
> - }
> + gfp_mask |= __GFP_WRITE;
> + if (fgp_flags & FGP_NOFS)
> + gfp_mask &= ~__GFP_FS;
>
> - page = __page_cache_alloc(cache_gfp_mask);
> + page = __page_cache_alloc(gfp_mask);
> if (!page)
> return NULL;
>
> @@ -1122,7 +1117,8 @@ no_page:
> if (fgp_flags & FGP_ACCESSED)
> __SetPageReferenced(page);
>
> - err = add_to_page_cache_lru(page, mapping, offset, radix_gfp_mask);
> + err = add_to_page_cache_lru(page, mapping, offset,
> + gfp_mask & GFP_RECLAIM_MASK);
> if (unlikely(err)) {
> page_cache_release(page);
> page = NULL;
> @@ -2443,8 +2439,7 @@ struct page *grab_cache_page_write_begin(struct address_space *mapping,
> fgp_flags |= FGP_NOFS;
>
> page = pagecache_get_page(mapping, index, fgp_flags,
> - mapping_gfp_mask(mapping),
> - GFP_KERNEL);
> + mapping_gfp_mask(mapping));
> if (page)
> wait_for_stable_page(page);
>
> --
> 2.1.4
>
> --
> Michal Hocko
> SUSE Labs
>
> --
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--
Michal Hocko
SUSE Labs