On Sun, 22 May 2011 15:27:41 -0700 (PDT) Hugh Dickins <hughd@xxxxxxxxxx> wrote: > 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. That should be true under i_mutex and perhaps other external locking. We could put some debug checks in there to catch any situation where ->index changed after the page was locked. > 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. I guess so. I doubt if it makes a measurable performance difference (except maybe in the case of small direct-io's?) but consistency is good. > - 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? err yes, that seems bogus now and was bogus at the time. I never trusted that s_maxbytes thing :) -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>