On 09/12/2012 10:03 AM, Hugh Dickins wrote: > On Mon, 13 Aug 2012, Xiao Guangrong wrote: > >> They are used to abstract the difference between NUMA enabled and NUMA disabled >> to make the code more readable >> >> Signed-off-by: Xiao Guangrong <xiaoguangrong@xxxxxxxxxxxxxxxxxx> >> --- >> mm/huge_memory.c | 166 ++++++++++++++++++++++++++++++++---------------------- >> 1 files changed, 98 insertions(+), 68 deletions(-) > > Hmm, that in itself is not necessarily an improvement. > > I'm a bit sceptical about this patch, > thp-introduce-khugepaged_prealloc_page-and-khugepaged_alloc_page.patch > in last Thursday's mmotm 2012-09-06-16-46. > > What brought me to look at it was hitting "BUG at mm/huge_memory.c:1842!" > running tmpfs kbuild swapping load (with memcg's memory.limit_in_bytes > forcing out to swap), while I happened to have CONFIG_NUMA=y. > > That's the VM_BUG_ON(*hpage) on entry to khugepaged_alloc_page(). I will look into it, thanks for your point it out. > > (If I'm honest, I'll admit I have Michel's "interval trees for anon rmap" > patches in on top, and so the line number was actually shifted to 1839: > but I don't believe his patches were in any way involved here, and > indeed I've not yet found a problem with them: they look very good.) > > I expect the BUG could quite easily be fixed up by making another call > to khugepaged_prealloc_page() from somewhere to free up the hpage; > but forgive me if I dislike using "prealloc" to free. > > I do agree with you that the several CONFIG_NUMA ifdefs dotted around > mm/huge_memory.c are regrettable, but I'm not at all sure that you're > improving the situation with this patch, which gives misleading names > to functions and moves the mmap_sem upping out of line. > > I think you need to revisit it: maybe not go so far (leaving a few > CONFIG_NUMAs behind, if they're not too bad), or maybe go further > (add a separate function for freeing in the NUMA case, instead of > using "prealloc"). I don't know what's best: have a play and see. Sorry for that, i will find a better way to do this. > > That's what I was intending to write yesterday. But overnight I > was running with this 9/12 backed out (I think 10,11,12 should be > independent), and found "BUG at mm/huge_memory.c:1835!" this morning. > > That's the VM_BUG_ON(*hpage) below #else in collapse_huge_page() > when 9/12 is reverted. > > So maybe 9/12 is just obscuring what was already a BUG, either earlier > in your series or elsewhere in mmotm (I've never seen it on 3.6-rc or > earlier releases, nor without CONFIG_NUMA). I've not spent any time > looking for it, maybe it's obvious - can you spot and fix it? Sure, will fix it as soon as possible. Thanks! -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>