Messages in this thread | | | Date | Sun, 22 May 2011 15:27:41 -0700 (PDT) | From | Hugh Dickins <> | Subject | Consistency of loops in mm/truncate.c? |
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Andrew,
I have a series aimed at 2.6.41 to remove mm/shmem.c's peculiar radix tree of swap entries, using slots in the file's standard radix_tree instead - prompted in part by https://lkml.org/lkml/2011/1/22/110
There's a patch to give shmem its own truncation loop, handling pages and swap entries in the same pass. For that I want to start from a copy of truncate_inode_page_range(), but notice some discrepancies between the different loops in mm/truncate.c, so want to standardize them first before copying.
The advancement of index is hard to follow: we rely upon page->index of an unlocked page persisting, yet we're ashamed of doing so, sometimes reading it again once locked. invalidate_mapping_pages() apologizes for this, but I think we should now just document that page->index is not modified until the page is freed.
invalidate_inode_pages2_range() has two sophistications not seen elsewhere, which 7afadfdc says were folded in by akpm (along with a page->index one):
- Don't look up more pages than we're going to use: seems a good thing for me to fold into truncate_inode_pages_range() and invalidate_mapping_pages() too.
- Check for the cursor wrapping at the end of the mapping: but with
#if BITS_PER_LONG==32 #define MAX_LFS_FILESIZE (((u64)PAGE_CACHE_SIZE << (BITS_PER_LONG-1))-1) #elif BITS_PER_LONG==64 #define MAX_LFS_FILESIZE 0x7fffffffffffffffUL #endif
I don't see how page->index + 1 would ever be 0, even if one or other of those "-1"s went away; so may I delete the "wrapped" case?
Thanks, Hugh
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