On Thu, 7 Jun 2007, Eric Dumazet wrote: > On Thu, 7 Jun 2007 07:59:47 -0400 > Kyle Moffett <[EMAIL PROTECTED]> wrote: > > > > Likewise there are a massive group of other libraries (especially > > user-interface and server related ones) that would really like to > > have support for creating file-descriptors without the top-level > > application closing them randomly (like several shells seem to). > > > > True, shells are sometimes quite strange. > > For example, bash uses file descriptor 255 (FD_CLOEXEC) > > When it forks a new process, child gets a file table with 256 slots. > > At exec() time, 255 is closed but file table doesnt shrink. > (shrinking is done at fork() time only) > > With fdmap, that means each process started by bash uses at least > 256 * sizeof(list_head) bytes, ie 4096 bytes on x86_64, even if only three > file-descriptors are opened (0,1,2) > > FD_CLOFORK should help here (BTW : current patch from Davide doesnt take this > into account and might need a change in fdmap_top_open_fd())
Yes, the CLOFORK flag is there, but it needs to be taken in account in fdmap_top_open_fd(). > Davide, are you sure we want FIFO for non sequential allocations ? > > This tends to use all the fmap slots, and not very cache friendly > if an app does a lot of [open(),...,close()] things. We already got a > perf drop because of RCUification of file freeing (FIFO mode instead > of LIFO given by kmalloc()/kfree()) > > If the idea behind this FIFO was security (ie not easy for an app to predict > next glibc file handle), we/glibc might use yet another FD_SECUREMODE flag, > wich ORed with O_NONSEQFD would ask to fdmap_newfd() to take the tail of > fmap->slist, not head. That was the reason, yes. If we agree that the base randomization is enough, we can use a LIFO. - Davide - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
