Messages in this thread Patch in this message | | | Date | Sun, 29 Jun 2008 01:24:18 +0100 (BST) | From | Hugh Dickins <> | Subject | [PATCH] splitlru: BDI_CAP_SWAP_BACKED |
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The split-lru patches put file and swap-backed pages on different lrus. shmem/tmpfs pages are awkward because they are swap-backed file pages. Since it's difficult to change lru midstream, they are treated as swap- backed throughout, with SetPageSwapBacked on allocation in shmem_getpage.
However, splice read (used by loop and sendfile) and readahead* allocate pages first, add_to_page_cache_lru, and then call into the filesystem through ->readpage. Under memory pressure, the shmem pages arrive at add_to_swap_cache and hit its BUG_ON(!PageSwapBacked(page)).
I've not yet found a better way to handle this than a "capability" flag in shmem_backing_dev_info, tested by add_to_page_cache_lru. And solely because it would look suspicious without it, set that BDI_CAP_SWAP_BACKED in swap_backing_dev_info also.
* readahead on shmem/tmpfs? I'd always thought ra_pages 0 prevented that; but in fact readahead(2), fadvise(POSIX_FADV_WILLNEED) and madvise(MADV_WILLNEED) all force_page_cache_readahead and get there.
Signed-off-by: Hugh Dickins <hugh@veritas.com> --- Should follow mmotm's vmscan-split-lru-lists-into-anon-file-sets.patch
include/linux/backing-dev.h | 13 +++++++++++++ mm/filemap.c | 13 ++++++++++++- mm/shmem.c | 2 +- mm/swap_state.c | 2 +- 4 files changed, 27 insertions(+), 3 deletions(-)
--- mmotm/include/linux/backing-dev.h 2008-05-03 21:55:10.000000000 +0100 +++ linux/include/linux/backing-dev.h 2008-06-27 17:02:45.000000000 +0100 @@ -175,6 +175,8 @@ int bdi_set_max_ratio(struct backing_dev * BDI_CAP_READ_MAP: Can be mapped for reading * BDI_CAP_WRITE_MAP: Can be mapped for writing * BDI_CAP_EXEC_MAP: Can be mapped for execution + * + * BDI_CAP_SWAP_BACKED: Count shmem/tmpfs objects as swap-backed. */ #define BDI_CAP_NO_ACCT_DIRTY 0x00000001 #define BDI_CAP_NO_WRITEBACK 0x00000002 @@ -184,6 +186,7 @@ int bdi_set_max_ratio(struct backing_dev #define BDI_CAP_WRITE_MAP 0x00000020 #define BDI_CAP_EXEC_MAP 0x00000040 #define BDI_CAP_NO_ACCT_WB 0x00000080 +#define BDI_CAP_SWAP_BACKED 0x00000100 #define BDI_CAP_VMFLAGS \ (BDI_CAP_READ_MAP | BDI_CAP_WRITE_MAP | BDI_CAP_EXEC_MAP) @@ -248,6 +251,11 @@ static inline bool bdi_cap_account_write BDI_CAP_NO_WRITEBACK)); } +static inline bool bdi_cap_swap_backed(struct backing_dev_info *bdi) +{ + return bdi->capabilities & BDI_CAP_SWAP_BACKED; +} + static inline bool mapping_cap_writeback_dirty(struct address_space *mapping) { return bdi_cap_writeback_dirty(mapping->backing_dev_info); @@ -258,4 +266,9 @@ static inline bool mapping_cap_account_d return bdi_cap_account_dirty(mapping->backing_dev_info); } +static inline bool mapping_cap_swap_backed(struct address_space *mapping) +{ + return bdi_cap_swap_backed(mapping->backing_dev_info); +} + #endif /* _LINUX_BACKING_DEV_H */ --- mmotm/mm/filemap.c 2008-06-27 13:39:20.000000000 +0100 +++ linux/mm/filemap.c 2008-06-27 18:16:07.000000000 +0100 @@ -493,7 +493,18 @@ EXPORT_SYMBOL(add_to_page_cache); int add_to_page_cache_lru(struct page *page, struct address_space *mapping, pgoff_t offset, gfp_t gfp_mask) { - int ret = add_to_page_cache(page, mapping, offset, gfp_mask); + int ret; + + /* + * Splice_read and readahead add shmem/tmpfs pages into the page cache + * before shmem_readpage has a chance to mark them as SwapBacked: they + * need to go on the active_anon lru below, and mem_cgroup_cache_charge + * (called in add_to_page_cache) needs to know where they're going too. + */ + if (mapping_cap_swap_backed(mapping)) + SetPageSwapBacked(page); + + ret = add_to_page_cache(page, mapping, offset, gfp_mask); if (ret == 0) { if (page_is_file_cache(page)) lru_cache_add_file(page); --- mmotm/mm/shmem.c 2008-06-27 13:39:20.000000000 +0100 +++ linux/mm/shmem.c 2008-06-27 17:25:41.000000000 +0100 @@ -201,7 +201,7 @@ static struct vm_operations_struct shmem static struct backing_dev_info shmem_backing_dev_info __read_mostly = { .ra_pages = 0, /* No readahead */ - .capabilities = BDI_CAP_NO_ACCT_AND_WRITEBACK, + .capabilities = BDI_CAP_NO_ACCT_AND_WRITEBACK | BDI_CAP_SWAP_BACKED, .unplug_io_fn = default_unplug_io_fn, }; --- mmotm/mm/swap_state.c 2008-06-27 13:39:20.000000000 +0100 +++ linux/mm/swap_state.c 2008-06-27 17:26:49.000000000 +0100 @@ -33,7 +33,7 @@ static const struct address_space_operat }; static struct backing_dev_info swap_backing_dev_info = { - .capabilities = BDI_CAP_NO_ACCT_AND_WRITEBACK, + .capabilities = BDI_CAP_NO_ACCT_AND_WRITEBACK | BDI_CAP_SWAP_BACKED, .unplug_io_fn = swap_unplug_io_fn, };
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