On Mon, 23 May 2011, Andrew Morton wrote: > On Sun, 22 May 2011 15:27:41 -0700 (PDT) > Hugh Dickins <hughd@xxxxxxxxxx> wrote: > > > > 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. Okay, I'll look into doing that; and adding a comment in the "page->mapping = NULL;" places in mm/filemap.c, explaining that we do need to leave page->index untouched. > > > 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. I guess it occasionally saves the radix_tree lookup from accessing a few unnecessary cachelines; not a big win, but I think better to add it where it's missing than remove it from the place you thought of it. > > > - 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 :) Right, I was wondering this morning whether we can always rely upon s_maxbytes: I was taking the SHMEM_MAX_INDEX check out of shmem_getpage(), but maybe some cases need it to stay. I'll do some more checking, but hope to remove those wrapped checks. Thanks for the confirmations, Hugh -- 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>